Multi-stream sensor for noninvasive measurement of blood constituents

ABSTRACT

The present disclosure relates to a sensor having a set of photodetectors that are arranged at various locations to enable the measurement of blood glucose. The photodetectors are arranged across multiple locations. For example, the detector may comprise multiple photodetector arrays that are arranged to have a sufficient difference in mean path length to allow for noise cancellation and noise reduction. Walls may be used in the detector to separate individual photodetectors and prevent mixing of detected optical radiation between the different locations on the measurement site. A window may also be employed to facilitate the passing of optical radiation at various wavelengths for measuring glucose in the tissue.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e)of the following U.S. Provisional Patent Applications:

Filing App. No. Date Title Attorney Docket 61/086,060 Aug. 4, 2008Multi-Stream Data Collection System For MLHUM.002PR Non-InvasiveMeasurement of Glucose and Other Analytes 61/086,108 Aug. 4, 2008Multi-Stream Sensor Front Ends for MLHUM.003PR Noninvasive Measurementof Glucose and Other Analytes 61/086,063 Aug. 4, 2008 Multi-StreamDetector For Noninvasive MLHUM.004PR Measurement Of Glucose And OtherAnalytes 61/086,057 Aug. 4, 2008 Multi-Stream Emitter For NoninvasiveMLHUM.005PR Measurement Of Glucose And Other Analytes 61/091,732 Aug.25, 2008 Sensor For Improving Measurement Of MLHUM.011PR BloodConstituents

This application is related to the following U.S. Patent Applications:

Filing App. No. Date Title Attorney Docket 12/497,528 Jul. 2, 2009 NoiseShielding for Noninvasive Device MLHUM.006A Contoured Protrusion forImproving 12/497,523 Jul. 2, 2009 Spectroscopic Measurement of BloodMLHUM.007A Constituents 12/498,506 Jul. 2, 2009 Heat Sink forNoninvasive Medical MLHUM.011A Sensor Unknown Herewith Multi-Stream DataCollection System for MLHUM.002A Non-Invasive Measurement of BloodConstituents Unknown Herewith Multi-Stream Sensor Front Ends forMLHUM.003A Non-Invasive Measurement of Blood Constituents UnknownHerewith Multi-Stream Emitter for Non-Invasive MLHUM.005A Measurement ofBlood Constituents

The foregoing applications are hereby incorporated by reference in theirentirety.

BACKGROUND

The standard of care in caregiver environments includes patientmonitoring through spectroscopic analysis using, for example, a pulseoximeter. Devices capable of spectroscopic analysis generally include alight source(s) transmitting optical radiation into or reflecting off ameasurement site, such as, body tissue carrying pulsing blood. Afterattenuation by tissue and fluids of the measurement site, aphotodetection device(s) detects the attenuated light and outputs adetector signal(s) responsive to the detected attenuated light. A signalprocessing device(s) process the detector(s) signal(s) and outputs ameasurement indicative of a blood constituent of interest, such asglucose, oxygen, met hemoglobin, total hemoglobin, other physiologicalparameters, or other data or combinations of data useful in determininga state or trend of wellness of a patient.

In noninvasive devices and methods, a sensor is often adapted toposition a finger proximate the light source and light detector. Forexample, noninvasive sensors often include a clothespin-shaped housingthat includes a contoured bed conforming generally to the shape of afinger.

SUMMARY

This disclosure describes embodiments of noninvasive methods, devices,and systems for measuring a blood analyte, such as oxygen, carbonmonoxide, methemoglobin, total hemoglobin, glucose, proteins, glucose,lipids, a percentage thereof (e.g., saturation) or for measuring manyother physiologically relevant patient characteristics. Thesecharacteristics can relate, for example, to pulse rate, hydration,trending information and analysis, and the like. In certain embodiments,a noninvasive sensor interfaces with tissue at a measurement site anddeforms the tissue in a way that increases signal gain in certaindesired wavelengths.

In some embodiments, a detector for the sensor may comprise a set ofphotodiodes that are arranged in a spatial configuration. This spatialconfiguration may allow, for example, signal analysis for measuringanalytes like glucose. In various embodiments, the detectors can bearranged across multiple locations in a spatial configuration. Thespatial configuration provides a geometry having a diversity of pathlengths among the detectors. For example, the detector in the sensor maycomprise multiple detectors that are arranged to have a sufficientdifference in mean path length to allow for noise cancellation and noisereduction.

In an embodiment, a physiological, noninvasive detector is configured todetect optical radiation from a tissue site. The detector comprises aset of photodetectors and a conversion processor. The set ofphotodetectors each provide a signal stream indicating optical radiationfrom the tissue site. The set of photodetectors are arranged in aspatial configuration that provides a variation in path lengths betweenat least some of the photodetectors. The conversion processor thatprovides information indicating an analyte in the tissue site based onratios of pairs of the signal streams.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages can beachieved in accordance with any particular embodiment of the inventionsdisclosed herein. Thus, the inventions disclosed herein can be embodiedor carried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as can be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers can be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate embodiments of the inventions described herein and not tolimit the scope thereof.

FIG. 1 illustrates a block diagram of an example data collection systemcapable of noninvasively measuring one or more blood analytes in amonitored patient, according to an embodiment of the disclosure;

FIGS. 2A-2D illustrate an exemplary handheld monitor and an exemplarynoninvasive optical sensor of the patient monitoring system of FIG. 1,according to embodiments of the disclosure;

FIGS. 3A-3C illustrate side and perspective views of an exemplarynoninvasive sensor housing including a finger bed protrusion and heatsink, according to an embodiment of the disclosure;

FIG. 3D illustrates a side view of another example noninvasive sensorhousing including a heat sink, according to an embodiment of thedisclosure;

FIG. 3E illustrates a perspective view of an example noninvasive sensordetector shell including example detectors, according to an embodimentof the disclosure;

FIG. 3F illustrates a side view of an example noninvasive sensor housingincluding a finger bed protrusion and heat sink, according to anembodiment of the disclosure;

FIGS. 4A through 4C illustrate top elevation, side and top perspectiveviews of an example protrusion, according to an embodiment of thedisclosure;

FIG. 5 illustrates an example graph depicting possible effects of aprotrusion on light transmittance, according to an embodiment of thedisclosure;

FIGS. 6A through 6D illustrate perspective, front elevation, side andtop views of another example protrusion, according to an embodiment ofthe disclosure;

FIG. 6E illustrates an example sensor incorporating the protrusion ofFIGS. 6A through 6D, according to an embodiment of the disclosure;

FIGS. 7A through 7B illustrate example arrangements of conductive glassthat may be employed in the system of FIG. 1, according to embodimentsof the disclosure.

FIGS. 8A through 8D illustrate an example top elevation view, sideviews, and a bottom elevation view of the conductive glass that may beemployed in the system of FIG. 1, according to embodiments of thedisclosure;

FIG. 9 shows example comparative results obtained by an embodiment of asensor;

FIGS. 10A and 10B illustrate comparative noise floors of variousembodiments of the present disclosure;

FIG. 11A illustrates a block diagram of some of the components that mayinclude an embodiment of a sensor, according to an embodiment of thedisclosure;

FIG. 11B illustrates a configuration of emitting optical radiation intoa measurement site for measuring blood constituents, according to anembodiment of the disclosure;

FIG. 11C illustrates another exemplary emitter that may be employed inthe sensor according to an embodiment of the disclosure;

FIG. 11D illustrates another exemplary emitter that may be employed inthe sensor according to an embodiment of the disclosure.

FIG. 12A illustrates an example detector portion that may be employed inan embodiment of a sensor, according to an embodiment of the disclosure;

FIGS. 12B through 12D illustrate exemplary arrangements of detectorsthat may be employed in an embodiment of the sensor, according to someembodiments of the disclosure;

FIGS. 12E through 12H illustrate exemplary structures of photodiodesthat may be employed in embodiments of the detectors, according to someembodiments of the disclosure;

FIG. 13 illustrates an example multi-stream operation of the system ofFIG. 1, according to an embodiment of the disclosure;

FIG. 14A illustrates another example detector portion having a partiallycylindrical protrusion that can be employed in an embodiment of asensor, according to an embodiment of the disclosure;

FIG. 14B depicts a front elevation view of the partially cylindricalprotrusion of FIG. 14A;

FIGS. 14C through 14E illustrate embodiments of a detector submount;

FIGS. 14F through 14H illustrate embodiment of portions of a detectorshell;

FIG. 14I illustrates a cutaway view of an embodiment of a sensor;

FIGS. 15A through 15F illustrate embodiments of sensors that includeheat sink features;

FIGS. 15G and 15H illustrate embodiments of connector features that canbe used with any of the sensors described herein;

FIG. 15I illustrates an exemplary architecture for atransimpedance-based front-end that may be employed in any of thesensors described herein;

FIG. 15J illustrates an exemplary noise model for configuring thetransimpedance-based front-ends shown in FIG. 15I;

FIG. 15K shows different architectures and layouts for variousembodiments of a sensor and its detectors;

FIG. 15L illustrates an exemplary architecture for aswitched-capacitor-based front-end that may be employed in any of thesensors described herein;

FIGS. 16A and 16B illustrate embodiments of disposable optical sensors;

FIG. 17 illustrates an exploded view of certain components of an examplesensor; and

FIGS. 18 through 22 illustrate various results obtained by an exemplarysensor of the disclosure.

DETAILED DESCRIPTION

The present disclosure generally relates to non-invasive medicaldevices. In some embodiments, a sensor can include photocommunicativecomponents, such as an emitter, a detector, and other components. Theemitter can include a plurality of sets of optical sources that, in anembodiment, are arranged together as a point source. The various opticalsources can emit a sequence of optical radiation pulses at differentwavelengths towards a measurement site, such as a patient's finger.

Detectors can then detect optical radiation from the measurement site.The optical sources and optical radiation detectors can operate at anyappropriate wavelength, including, as discussed herein, infrared, nearinfrared, visible light, and ultraviolet. In addition, the opticalsources and optical radiation detectors can operate at any appropriatewavelength, and such modifications to the embodiments desirable tooperate at any such wavelength will be apparent to those skilled in theart.

In certain embodiments, multiple detectors are employed and arranged ina spatial geometry. This spatial geometry provides a diversity of pathlengths among at least some of the detectors and allows for multiplebulk and pulsatile measurements that are robust. Each of the detectorscan provide a respective output stream based on the detected opticalradiation, or a sum of output streams can be provided from multipledetectors. In some embodiments, the sensor can also include othercomponents, such as one or more heat sinks and one or more thermistors.

The spatial configuration of the detectors provides a geometry having adiversity of path lengths among the detectors. For example, a detectorin the sensor may comprise multiple detectors that are arranged to havea sufficient difference in mean path length to allow for noisecancellation and noise reduction. In addition, walls may be used toseparate individual photodetectors and prevent mixing of detectedoptical radiation between the different locations on the measurementsite. A window may also be employed to facilitate the passing of opticalradiation at various wavelengths for measuring glucose in the tissue.

In the present disclosure, a sensor may measure various bloodconstituents or analytes noninvasively using spectroscopy and a recipeof various features. As disclosed herein, the sensor is capable ofnon-invasively measuring blood analytes, such as, glucose, totalhemoglobin, methemoglobin, oxygen content, and the like. In anembodiment, the spectroscopy used in the sensor can employ visible,infrared and near infrared wavelengths. The sensor may comprise anemitter, a detector, and other components. In some embodiments, thesensor may also comprise other components, such as one or more heatsinks and one or more thermistors.

In various embodiments, the sensor may also be coupled to one or morecompanion devices that process and/or display the sensor's output. Thecompanion devices may comprise various components, such as a sensorfront-end, a signal processor, a display, a network interface, a storagedevice or memory, etc.

The sensor may be integrated with the device, for example, into ahandheld unit comprising the sensor, a display and user controls. Inother embodiments, the sensor may communicate with one or moreprocessing devices. The communication may be via wire(s), cable(s), flexcircuit(s), wireless technologies, or other suitable analog or digitalcommunication methodologies and devices to perform those methodologies.Many of the foregoing arrangements allow the sensor to be attached tothe measurement site while the device is attached elsewhere on apatient, such as the patient's arm, or placed at a location near thepatient, such as a bed, shelf or table. The sensor or companion devicemay also provide outputs to a storage device or network interface.

Reference will now be made to the Figures to discuss embodiments of thepresent disclosure.

FIG. 1 illustrates an example of a data collection system 100. Incertain embodiments, the data collection system 100 noninvasivelymeasure a blood analyte, such as oxygen, carbon monoxide, methemoglobin,total hemoglobin, glucose, proteins, glucose, lipids, a percentagethereof (e.g., saturation) or for measuring many other physiologicallyrelevant patient characteristics. The system 100 can also measureadditional blood analytes and/or other physiological parameters usefulin determining a state or trend of wellness of a patient.

The data collection system 100 can be capable of measuring opticalradiation from the measurement site. For example, in some embodiments,the data collection system 100 can employ photodiodes defined in termsof area. In an embodiment, the area is from about 1 mm²-5 mm² (orhigher) that are capable of detecting about 100 nanoamps (nA) or less ofcurrent resulting from measured light at full scale. In addition tohaving its ordinary meaning, the phrase “at full scale” can mean lightsaturation of a photodiode amplifier (not shown). Of course, as would beunderstood by a person of skill in the art from the present disclosure,various other sizes and types of photodiodes can be used with theembodiments of the present disclosure.

The data collection system 100 can measure a range of approximatelyabout 2 nA to about 100 nA full scale. The data collection system 100can also include sensor front-ends that are capable of processing andamplifying current from the detector(s) at signal-to-noise ratios (SNRs)of about 100 decibels (dB) or more, such as about 120 dB in order tomeasure various desired analytes. The data collection system 100 canoperate with a lower SNR if less accuracy is desired for an analyte likeglucose.

The data collection system 100 can measure analyte concentrations,including glucose, at least in part by detecting light attenuated by ameasurement site 102. The measurement site 102 can be any location on apatient's body, such as a finger, foot, ear lobe, or the like. Forconvenience, this disclosure is described primarily in the context of afinger measurement site 102. However, the features of the embodimentsdisclosed herein can be used with other measurement sites 102.

In the depicted embodiment, the system 100 includes an optional tissuethickness adjuster or tissue shaper 105, which can include one or moreprotrusions, bumps, lenses, or other suitable tissue-shaping mechanisms.In certain embodiments, the tissue shaper 105 is a flat or substantiallyflat surface that can be positioned proximate the measurement site 102and that can apply sufficient pressure to cause the tissue of themeasurement site 102 to be flat or substantially flat. In otherembodiments, the tissue shaper 105 is a convex or substantially convexsurface with respect to the measurement site 102. Many otherconfigurations of the tissue shaper 105 are possible. Advantageously, incertain embodiments, the tissue shaper 105 reduces thickness of themeasurement site 102 while preventing or reducing occlusion at themeasurement site 102. Reducing thickness of the site can advantageouslyreduce the amount of attenuation of the light because there is lesstissue through which the light must travel. Shaping the tissue in to aconvex (or alternatively concave) surface can also provide more surfacearea from which light can be detected.

The embodiment of the data collection system 100 shown also includes anoptional noise shield 103. In an embodiment, the noise shield 103 can beadvantageously adapted to reduce electromagnetic noise while increasingthe transmittance of light from the measurement site 102 to one or moredetectors 106 (described below). For example, the noise shield 103 canadvantageously include a conductive coated glass or metal gridelectrically communicating with one or more other shields of the sensor101 or electrically grounded. In an embodiment where the noise shield103 includes conductive coated glass, the coating can advantageouslyinclude indium tin oxide. In an embodiment, the indium tin oxideincludes a surface resistivity ranging from approximately 30 ohms persquare inch to about 500 ohms per square inch. In an embodiment, theresistivity is approximately 30, 200, or 500 ohms per square inch. Aswould be understood by a person of skill in the art from the presentdisclosure, other resistivities can also be used which are less thanabout 30 ohms or more than about 500 ohms. Other conductive materialstransparent or substantially transparent to light can be used instead.

In some embodiments, the measurement site 102 is located somewhere alonga non-dominant arm or a non-dominant hand, e.g., a right-handed person'sleft arm or left hand. In some patients, the non-dominant arm or handcan have less musculature and higher fat content, which can result inless water content in that tissue of the patient. Tissue having lesswater content can provide less interference with the particularwavelengths that are absorbed in a useful manner by blood analytes likeglucose. Accordingly, in some embodiments, the data collection system100 can be used on a person's non-dominant hand or arm.

The data collection system 100 can include a sensor 101 (or multiplesensors) that is coupled to a processing device or physiological monitor109. In an embodiment, the sensor 101 and the monitor 109 are integratedtogether into a single unit. In another embodiment, the sensor 101 andthe monitor 109 are separate from each other and communicate one withanother in any suitable manner, such as via a wired or wirelessconnection. The sensor 101 and monitor 109 can be attachable anddetachable from each other for the convenience of the user or caregiver,for ease of storage, sterility issues, or the like. The sensor 101 andthe monitor 109 will now be further described.

In the depicted embodiment shown in FIG. 1, the sensor 101 includes anemitter 104, a tissue shaper 105, a set of detectors 106, and afront-end interface 108. The emitter 104 can serve as the source ofoptical radiation transmitted towards measurement site 102. As will bedescribed in further detail below, the emitter 104 can include one ormore sources of optical radiation, such as LEDs, laser diodes,incandescent bulbs with appropriate frequency-selective filters,combinations of the same, or the like. In an embodiment, the emitter 104includes sets of optical sources that are capable of emitting visibleand near-infrared optical radiation.

In some embodiments, the emitter 104 is used as a point optical source,and thus, the one or more optical sources of the emitter 104 can belocated within a close distance to each other, such as within about a 2mm to about 4 mm. The emitters 104 can be arranged in an array, such asis described in U.S. Publication No. 2006/0211924, filed Sep. 21, 2006,titled “Multiple Wavelength Sensor Emitters,” the disclosure of which ishereby incorporated by reference in its entirety. In particular, theemitters 104 can be arranged at least in part as described in paragraphs[0061] through [0068] of the aforementioned publication, whichparagraphs are hereby incorporated specifically by reference. Otherrelative spatial relationships can be used to arrange the emitters 104.

For analytes like glucose, currently available non-invasive techniquesoften attempt to employ light near the water absorbance minima at orabout 1600 nm. Typically, these devices and methods employ a singlewavelength or single band of wavelengths at or about 1600 nm. However,to date, these techniques have been unable to adequately consistentlymeasure analytes like glucose based on spectroscopy.

In contrast, the emitter 104 of the data collection system 100 can emit,in certain embodiments, combinations of optical radiation in variousbands of interest. For example, in some embodiments, for analytes likeglucose, the emitter 104 can emit optical radiation at three (3) or morewavelengths between about 1600 nm to about 1700 nm. In particular, theemitter 104 can emit optical radiation at or about 1610 nm, about 1640nm, and about 1665 nm. In some circumstances, the use of threewavelengths within about 1600 nm to about 1700 nm enable sufficient SNRsof about 100 dB, which can result in a measurement accuracy of about 20mg/dL or better for analytes like glucose.

In other embodiments, the emitter 104 can use two (2) wavelengths withinabout 1600 nm to about 1700 nm to advantageously enable SNRs of about 85dB, which can result in a measurement accuracy of about 25-30 mg/dL orbetter for analytes like glucose. Furthermore, in some embodiments, theemitter 104 can emit light at wavelengths above about 1670 nm.Measurements at these wavelengths can be advantageously used tocompensate or confirm the contribution of protein, water, and othernon-hemoglobin species exhibited in measurements for analytes likeglucose conducted between about 1600 nm and about 1700 nm. Of course,other wavelengths and combinations of wavelengths can be used to measureanalytes and/or to distinguish other types of tissue, fluids, tissueproperties, fluid properties, combinations of the same or the like.

For example, the emitter 104 can emit optical radiation across otherspectra for other analytes. In particular, the emitter 104 can employlight wavelengths to measure various blood analytes or percentages(e.g., saturation) thereof. For example, in one embodiment, the emitter104 can emit optical radiation in the form of pulses at wavelengthsabout 905 nm, about 1050 nm, about 1200 nm, about 1300 nm, about 1330nm, about 1610 nm, about 1640 nm, and about 1665 nm. In anotherembodiment, the emitter 104 can emit optical radiation ranging fromabout 860 nm to about 950 nm, about 950 nm to about 1100 nm, about 1100nm to about 1270 nm, about 1250 nm to about 1350 nm, about 1300 nm toabout 1360 nm, and about 1590 nm to about 1700 nm. Of course, theemitter 104 can transmit any of a variety of wavelengths of visible ornear-infrared optical radiation.

Due to the different responses of analytes to the different wavelengths,certain embodiments of the data collection system 100 can advantageouslyuse the measurements at these different wavelengths to improve theaccuracy of measurements. For example, the measurements of water fromvisible and infrared light can be used to compensate for waterabsorbance that is exhibited in the near-infrared wavelengths.

As briefly described above, the emitter 104 can include sets oflight-emitting diodes (LEDs) as its optical source. The emitter 104 canuse one or more top-emitting LEDs. In particular, in some embodiments,the emitter 104 can include top-emitting LEDs emitting light at about850 nm to 1350 nm.

The emitter 104 can also use super luminescent LEDs (SLEDs) orside-emitting LEDs. In some embodiments, the emitter 104 can employSLEDs or side-emitting LEDs to emit optical radiation at about 1600 nmto about 1800 nm. Emitter 104 can use SLEDs or side-emitting LEDs totransmit near infrared optical radiation because these types of sourcescan transmit at high power or relatively high power, e.g., about 40 mWto about 100 mW. This higher power capability can be useful tocompensate or overcome the greater attenuation of these wavelengths oflight in tissue and water. For example, the higher power emission caneffectively compensate and/or normalize the absorption signal for lightin the mentioned wavelengths to be similar in amplitude and/or effect asother wavelengths that can be detected by one or more photodetectorsafter absorption. However, the embodiments of the present disclosure donot necessarily require the use of high power optical sources. Forexample, some embodiments may be configured to measure analytes, such astotal hemoglobin (tHb), oxygen saturation (SpO₂), carboxyhemoglobin,methemoglobin, etc., without the use of high power optical sources likeside emitting LEDs. Instead, such embodiments may employ other types ofoptical sources, such as top emitting LEDs. Alternatively, the emitter104 can use other types of sources of optical radiation, such as a laserdiode, to emit near-infrared light into the measurement site 102.

In addition, in some embodiments, in order to assist in achieving acomparative balance of desired power output between the LEDs, some ofthe LEDs in the emitter 104 can have a filter or covering that reducesand/or cleans the optical radiation from particular LEDs or groups ofLEDs. For example, since some wavelengths of light can penetrate throughtissue relatively well, LEDs, such as some or all of the top-emittingLEDs can use a filter or covering, such as a cap or painted dye. Thiscan be useful in allowing the emitter 104 to use LEDs with a higheroutput and/or to equalize intensity of LEDs.

The data collection system 100 also includes a driver 111 that drivesthe emitter 104. The driver 111 can be a circuit or the like that iscontrolled by the monitor 109. For example, the driver 111 can providepulses of current to the emitter 104. In an embodiment, the driver 111drives the emitter 104 in a progressive fashion, such as in analternating manner. The driver 111 can drive the emitter 104 with aseries of pulses of about 1 milliwatt (mW) for some wavelengths that canpenetrate tissue relatively well and from about 40 mW to about 100 mWfor other wavelengths that tend to be significantly absorbed in tissue.A wide variety of other driving powers and driving methodologies can beused in various embodiments.

The driver 111 can be synchronized with other parts of the sensor 101and can minimize or reduce jitter in the timing of pulses of opticalradiation emitted from the emitter 104. In some embodiments, the driver111 is capable of driving the emitter 104 to emit optical radiation in apattern that varies by less than about 10 parts-per-million.

The detectors 106 capture and measure light from the measurement site102. For example, the detectors 106 can capture and measure lighttransmitted from the emitter 104 that has been attenuated or reflectedfrom the tissue in the measurement site 102. The detectors 106 canoutput a detector signal 107 responsive to the light captured ormeasured. The detectors 106 can be implemented using one or morephotodiodes, phototransistors, or the like.

In addition, the detectors 106 can be arranged with a spatialconfiguration to provide a variation of path lengths among at least someof the detectors 106. That is, some of the detectors 106 can have thesubstantially, or from the perspective of the processing algorithm,effectively, the same path length from the emitter 104. However,according to an embodiment, at least some of the detectors 106 can havea different path length from the emitter 104 relative to other of thedetectors 106. Variations in path lengths can be helpful in allowing theuse of a bulk signal stream from the detectors 106. In some embodiments,the detectors 106 may employ a linear spacing, a logarithmic spacing, ora two or three dimensional matrix of spacing or any other spacing schemein order to provide an appropriate variation in path lengths.

The front end interface 108 provides an interface that adapts the outputof the detectors 106, which is responsive to desired physiologicalparameters. For example, the front end interface 108 can adapt a signal107 received from one or more of the detectors 106 into a form that canbe processed by the monitor 109, for example, by a signal processor 110in the monitor 109. The front end interface 108 can have its componentsassembled in the sensor 101, in the monitor 109, in connecting cabling(if used), combinations of the same, or the like. The location of thefront end interface 108 can be chosen based on various factors includingspace desired for components, desired noise reductions or limits,desired heat reductions or limits, and the like.

The front end interface 108 can be coupled to the detectors 106 and tothe signal processor 110 using a bus, wire, electrical or optical cable,flex circuit, or some other form of signal connection. The front endinterface 108 can also be at least partially integrated with variouscomponents, such as the detectors 106. For example, the front endinterface 108 can include one or more integrated circuits that are onthe same circuit board as the detectors 106. Other configurations canalso be used.

The front end interface 108 can be implemented using one or moreamplifiers, such as transimpedance amplifiers, that are coupled to oneor more analog to digital converters (ADCs) (which can be in the monitor109), such as a sigma-delta ADC. A transimpedance-based front endinterface 108 can employ single-ended circuitry, differential circuitry,and/or a hybrid configuration. A transimpedance-based front endinterface 108 can be useful for its sampling rate capability and freedomin modulation/demodulation algorithms. For example, this type of frontend interface 108 can advantageously facilitate the sampling of the ADCsbeing synchronized with the pulses emitted from the emitter 104.

The ADC or ADCs can provide one or more outputs into multiple channelsof digital information for processing by the signal processor 110 of themonitor 109. Each channel can correspond to a signal output from adetector 106.

In some embodiments, a programmable gain amplifier (PGA) can be used incombination with a transimpedance-based front end interface 108. Forexample, the output of a transimpedance-based front end interface 108can be output to a PGA that is coupled with an ADC in the monitor 109. APGA can be useful in order to provide another level of amplification andcontrol of the stream of signals from the detectors 106. Alternatively,the PGA and ADC components can be integrated with thetransimpedance-based front end interface 108 in the sensor 101.

In another embodiment, the front end interface 108 can be implementedusing switched-capacitor circuits. A switched-capacitor-based front endinterface 108 can be useful for, in certain embodiments, itsresistor-free design and analog averaging properties. In addition, aswitched-capacitor-based front end interface 108 can be useful becauseit can provide a digital signal to the signal processor 110 in themonitor 109.

As shown in FIG. 1, the monitor 109 can include the signal processor 110and a user interface, such as a display 112. The monitor 109 can alsoinclude optional outputs alone or in combination with the display 112,such as a storage device 114 and a network interface 116. In anembodiment, the signal processor 110 includes processing logic thatdetermines measurements for desired analytes, such as glucose, based onthe signals received from the detectors 106. The signal processor 110can be implemented using one or more microprocessors or subprocessors(e.g., cores), digital signal processors, application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),combinations of the same, and the like.

The signal processor 110 can provide various signals that control theoperation of the sensor 101. For example, the signal processor 110 canprovide an emitter control signal to the driver 111. This control signalcan be useful in order to synchronize, minimize, or reduce jitter in thetiming of pulses emitted from the emitter 104. Accordingly, this controlsignal can be useful in order to cause optical radiation pulses emittedfrom the emitter 104 to follow a precise timing and consistent pattern.For example, when a transimpedance-based front end interface 108 isused, the control signal from the signal processor 110 can providesynchronization with the ADC in order to avoid aliasing, cross-talk, andthe like. As also shown, an optional memory 113 can be included in thefront-end interface 108 and/or in the signal processor 110. This memory113 can serve as a buffer or storage location for the front-endinterface 108 and/or the signal processor 110, among other uses.

The user interface 112 can provide an output, e.g., on a display, forpresentation to a user of the data collection system 100. The userinterface 112 can be implemented as a touch-screen display, an LCDdisplay, an organic LED display, or the like. In addition, the userinterface 112 can be manipulated to allow for measurement on thenon-dominant side of patient. For example, the user interface 112 caninclude a flip screen, a screen that can be moved from one side toanother on the monitor 109, or can include an ability to reorient itsdisplay indicia responsive to user input or device orientation. Inalternative embodiments, the data collection system 100 can be providedwithout a user interface 112 and can simply provide an output signal toa separate display or system.

A storage device 114 and a network interface 116 represent otheroptional output connections that can be included in the monitor 109. Thestorage device 114 can include any computer-readable medium, such as amemory device, hard disk storage, EEPROM, flash drive, or the like. Thevarious software and/or firmware applications can be stored in thestorage device 114, which can be executed by the signal processor 110 oranother processor of the monitor 109. The network interface 116 can be aserial bus port (RS-232/RS-485), a Universal Serial Bus (USB) port, anEthernet port, a wireless interface (e.g., WiFi such as any 802.1xinterface, including an internal wireless card), or other suitablecommunication device(s) that allows the monitor 109 to communicate andshare data with other devices. The monitor 109 can also include variousother components not shown, such as a microprocessor, graphicsprocessor, or controller to output the user interface 112, to controldata communications, to compute data trending, or to perform otheroperations.

Although not shown in the depicted embodiment, the data collectionsystem 100 can include various other components or can be configured indifferent ways. For example, the sensor 101 can have both the emitter104 and detectors 106 on the same side of the measurement site 102 anduse reflectance to measure analytes. The data collection system 100 canalso include a sensor that measures the power of light emitted from theemitter 104.

FIGS. 2A through 2D illustrate example monitoring devices 200 in whichthe data collection system 100 can be housed. Advantageously, in certainembodiments, some or all of the example monitoring devices 200 shown canhave a shape and size that allows a user to operate it with a singlehand or attach it, for example, to a patient's body or limb. Althoughseveral examples are shown, many other monitoring device configurationscan be used to house the data collection system 100. In addition,certain of the features of the monitoring devices 200 shown in FIGS. 2Athrough 2D can be combined with features of the other monitoring devices200 shown.

Referring specifically to FIG. 2A, an example monitoring device 200A isshown, in which a sensor 201 a and a monitor 209 a are integrated into asingle unit. The monitoring device 200A shown is a handheld or portabledevice that can measure glucose and other analytes in a patient'sfinger. The sensor 201 a includes an emitter shell 204 a and a detectorshell 206 a. The depicted embodiment of the monitoring device 200A alsoincludes various control buttons 208 a and a display 210 a.

The sensor 201 a can be constructed of white material used forreflective purposes (such as white silicone or plastic), which canincrease the usable signal at the detector 106 by forcing light backinto the sensor 201 a. Pads in the emitter shell 204 a and the detectorshell 206 a can contain separated windows to prevent or reduce mixing oflight signals, for example, from distinct quadrants on a patient'sfinger. In addition, these pads can be made of a relatively softmaterial, such as a gel or foam, in order to conform to the shape, forexample, of a patient's finger. The emitter shell 204 a and the detectorshell 206 a can also include absorbing black or grey material portionsto prevent or reduce ambient light from entering into the sensor 201 a.

In some embodiments, some or all portions of the emitter shell 204 aand/or detector shell 206 a can be detachable and/or disposable. Forexample, some or all portions of the shells 204 a and 206 a can beremovable pieces. The removability of the shells 204 a and 206 a can beuseful for sanitary purposes or for sizing the sensor 201 a to differentpatients. The monitor 209 a can include a fitting, slot, magnet, orother connecting mechanism to allow the sensor 201 c to be removablyattached to the monitor 209 a.

The monitoring device 200 a also includes optional control buttons 208 aand a display 210 a that can allow the user to control the operation ofthe device. For example, a user can operate the control buttons 208 a toview one or more measurements of various analytes, such as glucose. Inaddition, the user can operate the control buttons 208 a to view otherforms of information, such as graphs, histograms, measurement data,trend measurement data, parameter combination views, wellnessindications, and the like. Many parameters, trends, alarms and parameterdisplays could be output to the display 210 a, such as those that arecommercially available through a wide variety of noninvasive monitoringdevices from Masimo® Corporation of Irvine, Calif.

Furthermore, the controls 208 a and/or display 210 a can providefunctionality for the user to manipulate settings of the monitoringdevice 200 a, such as alarm settings, emitter settings, detectorsettings, and the like. The monitoring device 200 a can employ any of avariety of user interface designs, such as frames, menus, touch-screens,and any type of button.

FIG. 2B illustrates another example of a monitoring device 200B. In thedepicted embodiment, the monitoring device 200B includes a finger clipsensor 201 b connected to a monitor 209 b via a cable 212. In theembodiment shown, the monitor 209 b includes a display 210 b, controlbuttons 208 b and a power button. Moreover, the monitor 209 b canadvantageously include electronic processing, signal processing, anddata storage devices capable of receiving signal data from said sensor201 b, processing the signal data to determine one or more outputmeasurement values indicative of one or more physiological parameters ofa monitored patient, and displaying the measurement values, trends ofthe measurement values, combinations of measurement values, and thelike.

The cable 212 connecting the sensor 201 b and the monitor 209 b can beimplemented using one or more wires, optical fiber, flex circuits, orthe like. In some embodiments, the cable 212 can employ twisted pairs ofconductors in order to minimize or reduce cross-talk of data transmittedfrom the sensor 201 b to the monitor 209 b. Various lengths of the cable212 can be employed to allow for separation between the sensor 201 b andthe monitor 209 b. The cable 212 can be fitted with a connector (male orfemale) on either end of the cable 212 so that the sensor 201 b and themonitor 209 b can be connected and disconnected from each other.Alternatively, the sensor 201 b and the monitor 209 b can be coupledtogether via a wireless communication link, such as an infrared link,radio frequency channel, or any other wireless communication protocoland channel.

The monitor 209 b can be attached to the patient. For example, themonitor 209 b can include a belt clip or straps (see, e.g., FIG. 2C)that facilitate attachment to a patient's belt, arm, leg, or the like.The monitor 209 b can also include a fitting, slot, magnet, LEMOsnap-click connector, or other connecting mechanism to allow the cable212 and sensor 201 b to be attached to the monitor 209B.

The monitor 209 b can also include other components, such as a speaker,power button, removable storage or memory (e.g., a flash card slot), anAC power port, and one or more network interfaces, such as a universalserial bus interface or an Ethernet port. For example, the monitor 209 bcan include a display 210 b that can indicate a measurement for glucose,for example, in mg/dL. Other analytes and forms of display can alsoappear on the monitor 209 b.

In addition, although a single sensor 201 b with a single monitor 209 bis shown, different combinations of sensors and device pairings can beimplemented. For example, multiple sensors can be provided for aplurality of differing patient types or measurement sites or evenpatient fingers.

FIG. 2C illustrates yet another example of monitoring device 200C thatcan house the data collection system 100. Like the monitoring device200B, the monitoring device 200C includes a finger clip sensor 201 cconnected to a monitor 209 c via a cable 212. The cable 212 can have allof the features described above with respect to FIG. 2B. The monitor 209c can include all of the features of the monitor 200B described above.For example, the monitor 209 c includes buttons 208 c and a display 210c. The monitor 209 c shown also includes straps 214 c that allow themonitor 209 c to be attached to a patient's limb or the like.

FIG. 2D illustrates yet another example of monitoring device 200D thatcan house the data collection system 100. Like the monitoring devices200B and 200C, the monitoring device 200D includes a finger clip sensor201 d connected to a monitor 209 d via a cable 212. The cable 212 canhave all of the features described above with respect to FIG. 2B. Inaddition to having some or all of the features described above withrespect to FIGS. 2B and 2C, the monitoring device 200D includes anoptional universal serial bus (USB) port 216 and an Ethernet port 218.The USB port 216 and the Ethernet port 218 can be used, for example, totransfer information between the monitor 209 d and a computer (notshown) via a cable. Software stored on the computer can providefunctionality for a user to, for example, view physiological data andtrends, adjust settings and download firmware updates to the monitor 209b, and perform a variety of other functions. The USB port 216 and theEthernet port 218 can be included with the other monitoring devices200A, 200B, and 200C described above.

FIGS. 3A through 3C illustrate more detailed examples of embodiments ofa sensor 301 a. The sensor 301 a shown can include all of the featuresof the sensors 100 and 200 described above.

Referring to FIG. 3A, the sensor 301 a in the depicted embodiment is aclothespin-shaped clip sensor that includes an enclosure 302 a forreceiving a patient's finger. The enclosure 302 a is formed by an uppersection or emitter shell 304 a, which is pivotably connected with alower section or detector shell 306 a. The emitter shell 304 a can bebiased with the detector shell 306 a to close together around a pivotpoint 303 a and thereby sandwich finger tissue between the emitter anddetector shells 304 a, 306 a.

In an embodiment, the pivot point 303 a advantageously includes a pivotcapable of adjusting the relationship between the emitter and detectorshells 304 a, 306 a to effectively level the sections when applied to atissue site. In another embodiment, the sensor 301 a includes some orall features of the finger clip described in U.S. Publication No.2006/0211924, incorporated above, such as a spring that causes fingerclip forces to be distributed along the finger. Paragraphs

through [0105], which describe this feature, are hereby specificallyincorporated by reference.

The emitter shell 304 a can position and house various emittercomponents of the sensor 301 a. It can be constructed of reflectivematerial (e.g., white silicone or plastic) and/or can be metallic orinclude metalicized plastic (e.g., including carbon and aluminum) topossibly serve as a heat sink. The emitter shell 304 a can also includeabsorbing opaque material, such as, for example, black or grey coloredmaterial, at various areas, such as on one or more flaps 307 a, toreduce ambient light entering the sensor 301 a.

The detector shell 306 a can position and house one or more detectorportions of the sensor 301 a. The detector shell 306 a can beconstructed of reflective material, such as white silicone or plastic.As noted, such materials can increase the usable signal at a detector byforcing light back into the tissue and measurement site (see FIG. 1).The detector shell 306 a can also include absorbing opaque material atvarious areas, such as lower area 308 a, to reduce ambient lightentering the sensor 301 a.

Referring to FIGS. 3B and 3C, an example of finger bed 310 is shown inthe sensor 301 b. The finger bed 310 includes a generally curved surfaceshaped generally to receive tissue, such as a human digit. The fingerbed 310 includes one or more ridges or channels 314. Each of the ridges314 has a generally convex shape that can facilitate increasing tractionor gripping of the patient's finger to the finger bed. Advantageously,the ridges 314 can improve the accuracy of spectroscopic analysis incertain embodiments by reducing noise that can result from a measurementsite moving or shaking loose inside of the sensor 301 a. The ridges 314can be made from reflective or opaque materials in some embodiments tofurther increase SNR. In other implementations, other surface shapes canbe used, such as, for example, generally flat, concave, or convex fingerbeds 310.

Finger bed 310 can also include an embodiment of a tissue thicknessadjuster or protrusion 305. The protrusion 305 includes a measurementsite contact area 370 (see FIG. 3C) that can contact body tissue of ameasurement site. The protrusion 305 can be removed from or integratedwith the finger bed 310. Interchangeable, different shaped protrusions305 can also be provided, which can correspond to different fingershapes, characteristics, opacity, sizes, or the like.

Referring specifically to FIG. 3C, the contact area 370 of theprotrusion 305 can include openings or windows 320, 321, 322, and 323.When light from a measurement site passes through the windows 320, 321,322, and 323, the light can reach one or more photodetectors (see FIG.3E). In an embodiment, the windows 320, 321, 322, and 323 mirrorspecific detector placements layouts such that light can impinge throughthe protrusion 305 onto the photodetectors. Any number of windows 320,321, 322, and 323 can be employed in the protrusion 305 to allow lightto pass from the measurement site to the photodetectors.

The windows 320, 321, 322, and 323 can also include shielding, such asan embedded grid of wiring or a conductive glass coating, to reducenoise from ambient light or other electromagnetic noise. The windows320, 321, 322, and 323 can be made from materials, such as plastic orglass. In some embodiments, the windows 320, 321, 322, and 323 can beconstructed from conductive glass, such as indium tin oxide (ITO) coatedglass. Conductive glass can be useful because its shielding istransparent, and thus allows for a larger aperture versus a window withan embedded grid of wiring. In addition, in certain embodiments, theconductive glass does not need openings in its shielding (since it istransparent), which enhances its shielding performance. For example,some embodiments that employ the conductive glass can attain up to anabout 40% to about 50% greater signal than non-conductive glass with ashielding grid. In addition, in some embodiments, conductive glass canbe useful for shielding noise from a greater variety of directions thannon-conductive glass with a shielding grid.

Turning to FIG. 3B, the sensor 301 a can also include a shielding 315 a,such as a metal cage, box, metal sheet, perforated metal sheet, a metallayer on a non-metal material, or the like. The shielding 315 a isprovided in the depicted embodiment below or embedded within theprotrusion 305 to reduce noise. The shielding 315 a can be constructedfrom a conductive material, such as copper. The shielding 315 a caninclude one or more openings or windows (not shown). The windows can bemade from glass or plastic to thereby allow light that has passedthrough the windows 320, 321, 322, and 323 on an external surface of theprotrusion 305 (see FIG. 3C) to pass through to one or morephotodetectors that can be enclosed or provided below (see FIG. 3E).

In some embodiments, the shielding cage for shielding 315 a can beconstructed in a single manufactured component with or without the useof conductive glass. This form of construction may be useful in order toreduce costs of manufacture as well as assist in quality control of thecomponents. Furthermore, the shielding cage can also be used to housevarious other components, such as sigma delta components for variousembodiments of front end interfaces 108.

In an embodiment, the photodetectors can be positioned within ordirectly beneath the protrusion 305 (see FIG. 3E). In such cases, themean optical path length from the emitters to the detectors can bereduced and the accuracy of blood analyte measurement can increase. Forexample, in one embodiment, a convex bump of about 1 mm to about 3 mm inheight and about 10 mm² to about 60 mm² was found to help signalstrength by about an order of magnitude versus other shapes. Of courseother dimensions and sizes can be employed in other embodiments.Depending on the properties desired, the length, width, and height ofthe protrusion 305 can be selected. In making such determinations,consideration can be made of protrusion's 305 effect on blood flow atthe measurement site and mean path length for optical radiation passingthrough openings 320, 321, 322, and 323. Patient comfort can also beconsidered in determining the size and shape of the protrusion.

In an embodiment, the protrusion 305 can include a pliant material,including soft plastic or rubber, which can somewhat conform to theshape of a measurement site. Pliant materials can improve patientcomfort and tactility by conforming the measurement site contact area307 to the measurement site. Additionally, pliant materials can minimizeor reduce noise, such as ambient light. Alternatively, the protrusion305 can be made from a rigid material, such as hard plastic or metal.

Rigid materials can improve measurement accuracy of a blood analyte byconforming the measurement site to the contact area 370. The contactarea 307 can be an ideal shape for improving accuracy or reducing noise.Selecting a material for the protrusion 305 can include consideration ofmaterials that do not significantly alter blood flow at the measurementsite. The protrusion 305 and the contact area 307 can include acombination of materials with various characteristics.

The contact area 307 serves as a contact surface for the measurementsite. For example, in some embodiments, the contact area 307 can beshaped for contact with a patient's finger. Accordingly, the contactarea 307 can be sized and shaped for different sizes of fingers. Thecontact area 307 can be constructed of different materials forreflective purposes as well as for the comfort of the patient. Forexample, the contact area 307 can be constructed from materials havingvarious hardness and textures, such as plastic, gel, foam, and the like.

The formulas and analysis that follow with respect to FIG. 5 provideinsight into how selecting these variables can alter transmittance andintensity gain of optical radiation that has been applied to themeasurement site. These examples do not limit the scope of thisdisclosure.

Referring to FIG. 5, a plot 500 is shown that illustrates examples ofeffects of embodiments of the protrusion 305 on the SNR at variouswavelengths of light. As described above, the protrusion 305 can assistin conforming the tissue and effectively reduce its mean path length. Insome instances, this effect by the protrusion 305 can have significantimpact on increasing the SNR.

According to the Beer Lambert law, a transmittance of light (I) can beexpressed as follows: I=I_(o)*e^(−m*b*c), where I_(o) is the initialpower of light being transmitted, m is the path length traveled by thelight, and the component “b*c” corresponds to the bulk absorption of thelight at a specific wavelength of light. For light at about 1600 nm toabout 1700 nm, for example, the bulk absorption component is generallyaround 0.7 mm⁻¹. Assuming a typical finger thickness of about 12 mm anda mean path length of 20 mm due to tissue scattering, thenI=I_(o)*e^((−20*0.7)).

In an embodiment where the protrusion 305 is a convex bump, thethickness of the finger can be reduced to 10 mm (from 12 mm) for somefingers and the effective light mean path is reduced to about 16.6 mmfrom 20 mm (see box 510). This results in a new transmittance,I₁=I_(o)*e^((−16.6*0.7)). A curve for a typical finger (having a meanpath length of 20 mm) across various wavelengths is shown in the plot500 of FIG. 5. The plot 500 illustrates potential effects of theprotrusion 305 on the transmittance. As illustrated, comparing I and I₁results in an intensity gain of e^((−16.6*0.7))/e^((−20*0.7)), which isabout a 10 times increase for light in the about 1600 nm to about 1700nm range. Such an increase can affect the SNR at which the sensor canoperate. The foregoing gains can be due at least in part to the about1600 nm to about 1700 nm range having high values in bulk absorptions(water, protein, and the like), e.g., about 0.7 mm⁻¹. The plot 500 alsoshows improvements in the visible/near-infrared range (about 600 nm toabout 1300 nm).

Turning again to FIGS. 3A through 3C, an example heat sink 350 a is alsoshown. The heat sink 350 a can be attached to, or protrude from an outersurface of, the sensor 301 a, thereby providing increased ability forvarious sensor components to dissipate excess heat. By being on theouter surface of the sensor 301 a in certain embodiments, the heat sink350 a can be exposed to the air and thereby facilitate more efficientcooling. In an embodiment, one or more of the emitters (see FIG. 1)generate sufficient heat that inclusion of the heat sink 350 a canadvantageously allows the sensor 301 a to remain safely cooled. The heatsink 350 a can include one or more materials that help dissipate heat,such as, for example, aluminum, steel, copper, carbon, combinations ofthe same, or the like. For example, in some embodiments, the emittershell 304 a can include a heat conducting material that is also readilyand relatively inexpensively moldable into desired shapes and forms.

In some embodiments, the heat sink 350 a includes metalicized plastic.The metalicized plastic can include aluminum and carbon, for example.The material can allow for improved thermal conductivity anddiffusivity, which can increase commercial viability of the heat sink.In some embodiments, the material selected to construct the heat sink350 a can include a thermally conductive liquid crystalline polymer,such as CoolPoly® D5506, commercially available from Cool Polymers®,Inc. of Warwick, R.I. Such a material can be selected for itselectrically non-conductive and dielectric properties so as, forexample, to aid in electrical shielding. In an embodiment, the heat sink350 a provides improved heat transfer properties when the sensor 301 ais active for short intervals of less than a full day's use. In anembodiment, the heat sink 350 a can advantageously provide improved heattransfers in about three (3) to about four (4) minute intervals, forexample, although a heat sink 350 a can be selected that performseffectively in shorter or longer intervals.

Moreover, the heat sink 350 a can have different shapes andconfigurations for aesthetic as well as for functional purposes. In anembodiment, the heat sink is configured to maximize heat dissipation,for example, by maximizing surface area. In an embodiment, the heat sink350 a is molded into a generally curved surface and includes one or morefins, undulations, grooves, or channels. The example heat sink 350 ashown includes fins 351 a (see FIG. 3A).

An alternative shape of a sensor 301 b and heat sink 350 b is shown inFIG. 3D. The sensor 301 b can include some or all of the features of thesensor 301 a. For example, the sensor 301 b includes an enclosure 302 bformed by an emitter shell 304 b and a detector shell 306 b, pivotablyconnected about a pivot 303 a. The emitter shell 304 b can also includeabsorbing opaque material on one or more flaps 307 b, and the detectorshell 306 a can also include absorbing opaque material at various areas,such as lower area 308 b.

However, the shape of the sensor 301 b is different in this embodiment.In particular, the heat sink 350 b includes comb protrusions 351 b. Thecomb protrusions 351 b are exposed to the air in a similar manner to thefins 351 a of the heat sink 350 a, thereby facilitating efficientcooling of the sensor 301 b.

FIG. 3E illustrates a more detailed example of a detector shell 306 b ofthe sensor 301 b. The features described with respect to the detectorshell 306 b can also be used with the detector shell 306 a of the sensor301 a.

As shown, the detector shell 306 b includes detectors 316. The detectors316 can have a predetermined spacing 340 from each other, or a spatialrelationship among one another that results in a spatial configuration.This spatial configuration can purposefully create a variation of pathlengths among detectors 316 and the emitter discussed above.

In the depicted embodiment, the detector shell 316 can hold multiple(e.g., two, three, four, etc.) photodiode arrays that are arranged in atwo-dimensional grid pattern. Multiple photodiode arrays can also beuseful to detect light piping (e.g., light that bypasses measurementsite 102). In the detector shell 316, walls can be provided to separatethe individual photodiode arrays to prevent or reduce mixing of lightsignals from distinct quadrants. In addition, the detector shell 316 canbe covered by windows of transparent material, such as glass, plastic,or the like, to allow maximum or increased transmission of power lightcaptured. In various embodiments, the transparent materials used canalso be partially transparent or translucent or can otherwise pass someor all of the optical radiation passing through them. As noted, thiswindow can include some shielding in the form of an embedded grid ofwiring, or a conductive layer or coating.

As further illustrated by FIG. 3E, the detectors 316 can have a spatialconfiguration of a grid. However, the detectors 316 can be arranged inother configurations that vary the path length. For example, thedetectors 316 can be arranged in a linear array, a logarithmic array, atwo-dimensional array, a zig-zag pattern, or the like. Furthermore, anynumber of the detectors 316 can be employed in certain embodiments.

FIG. 3F illustrates another embodiment of a sensor 301 f. The sensor 301f can include some or all of the features of the sensor 301 a of FIG. 3Adescribed above. For example, the sensor 301 f includes an enclosure 302f formed by an upper section or emitter shell 304 f, which is pivotablyconnected with a lower section or detector shell 306 f around a pivotpoint 303 f. The emitter shell 304 f can also include absorbing opaquematerial on various areas, such as on one or more flaps 307 f, to reduceambient light entering the sensor 301 f. The detector shell 306 f canalso include absorbing opaque material at various areas, such as a lowerarea 308 f. The sensor 301 f also includes a heat sink 350 f, whichincludes fins 351 f.

In addition to these features, the sensor 301 f includes a flex circuitcover 360, which can be made of plastic or another suitable material.The flex circuit cover 360 can cover and thereby protect a flex circuit(not shown) that extends from the emitter shell 304 f to the detectorshell 306 f. An example of such a flex circuit is illustrated in U.S.Publication No. 2006/0211924, incorporated above (see FIG. 46 andassociated description, which is hereby specifically incorporated byreference). The flex circuit cover 360 is shown in more detail below inFIG. 17.

In addition, sensors 301 a-f has extra length—extends to second joint onfinger—Easier to place, harder to move due to cable, better for lightpiping

FIGS. 4A through 4C illustrate example arrangements of a protrusion 405,which is an embodiment of the protrusion 305 described above. In anembodiment, the protrusion 405 can include a measurement site contactarea 470. The measurement site contact area 470 can include a surfacethat molds body tissue of a measurement site, such as a finger, into aflat or relatively flat surface.

The protrusion 405 can have dimensions that are suitable for ameasurement site such as a patient's finger. As shown, the protrusion405 can have a length 400, a width 410, and a height 430. The length 400can be from about 9 to about 11 millimeters, e.g., about 10 millimeters.The width 410 can be from about 7 to about 9 millimeters, e.g., about 8millimeters. The height 430 can be from about 0.5 millimeters to about 3millimeters, e.g., about 2 millimeters. In an embodiment, the dimensions400, 410, and 430 can be selected such that the measurement site contactarea 470 includes an area of about 80 square millimeters, althoughlarger and smaller areas can be used for different sized tissue for anadult, an adolescent, or infant, or for other considerations.

The measurement site contact area 470 can also include differentlyshaped surfaces that conform the measurement site into different shapes.For example, the measurement site contact area 470 can be generallycurved and/or convex with respect to the measurement site. Themeasurement site contact area 470 can be other shapes that reduce oreven minimize air between the protrusion 405 and or the measurementsite. Additionally, the surface pattern of the measurement site contactarea 470 can vary from smooth to bumpy, e.g., to provide varying levelsof grip.

In FIGS. 4A and 4C, openings or windows 420, 421, 422, and 423 caninclude a wide variety of shapes and sizes, including for example,generally square, circular, triangular, or combinations thereof. Thewindows 420, 421, 422, and 423 can be of non-uniform shapes and sizes.As shown, the windows 420, 421, 422, and 423 can be evenly spaced out ina grid like arrangement. Other arrangements or patterns of arranging thewindows 420, 421, 422, and 423 are possible. For example, the windows420, 421, 422, and 423 can be placed in a triangular, circular, orlinear arrangement. In some embodiments, the windows 420, 421, 422, and423 can be placed at different heights with respect to the finger bed310 of FIG. 3. The windows 420, 421, 422, and 423 can also mimic orapproximately mimic a configuration of, or even house, a plurality ofdetectors.

FIGS. 6A through 6D illustrate another embodiment of a protrusion 605that can be used as the tissue shaper 105 described above or in place ofthe protrusions 305, 405 described above. The depicted protrusion 605 isa partially cylindrical lens having a partial cylinder 608 and anextension 610. The partial cylinder 608 can be a half cylinder in someembodiments; however, a smaller or greater portion than half of acylinder can be used. Advantageously, in certain embodiments, thepartially cylindrical protrusion 605 focuses light onto a smaller area,such that fewer detectors can be used to detect the light attenuated bya measurement site.

FIG. 6A illustrates a perspective view of the partially cylindricalprotrusion 605. FIG. 6B illustrates a front elevation view of thepartially cylindrical protrusion 605. FIG. 6C illustrates a side view ofthe partially cylindrical protrusion 605. FIG. 6D illustrates a top viewof the partially cylindrical protrusion 605.

Advantageously, in certain embodiments, placing the partiallycylindrical protrusion 605 over the photodiodes in any of the sensorsdescribed above adds multiple benefits to any of the sensors describedabove. In one embodiment, the partially cylindrical protrusion 605penetrates into the tissue and reduces the path length of the lighttraveling in the tissue, similar to the protrusions described above.

The partially cylindrical protrusion 605 can also collect light from alarge surface and focus down the light to a smaller area. As a result,in certain embodiments, signal strength per area of the photodiode canbe increased. The partially cylindrical protrusion 605 can thereforefacilitate a lower cost sensor because, in certain embodiments, lessphotodiode area can be used to obtain the same signal strength. Lessphotodiode area can be realized by using smaller photodiodes or fewerphotodiodes (see, e.g., FIG. 14). If fewer or smaller photodiodes areused, the partially cylindrical protrusion 605 can also facilitate animproved SNR of the sensor because fewer or smaller photodiodes can haveless dark current.

The dimensions of the partially cylindrical protrusion 605 can varybased on, for instance, a number of photodiodes used with the sensor.Referring to FIG. 6C, the overall height of the partially cylindricalprotrusion 605 (measurement “a”) in some implementations is about 1 toabout 3 mm. A height in this range can allow the partially cylindricalprotrusion 605 to penetrate into the pad of the finger or other tissueand reduce the distance that light travels through the tissue. Otherheights, however, of the partially cylindrical protrusion 605 can alsoaccomplish this objective. For example, the chosen height of thepartially cylindrical protrusion 605 can be selected based on the sizeof the measurement site, whether the patient is an adult or child, andso on. In an embodiment, the height of the protrusion 605 is chosen toprovide as much tissue thickness reduction as possible while reducing orpreventing occlusion of blood vessels in the tissue.

Referring to FIG. 6D, the width of the partially cylindrical protrusion605 (measurement “b”) can be about 3 to about 5 mm. In one embodiment,the width is about 4 mm. In one embodiment, a width in this rangeprovides good penetration of the partially cylindrical protrusion 605into the tissue to reduce the path length of the light. Other widths,however, of the partially cylindrical protrusion 605 can also accomplishthis objective. For example, the width of the partially cylindricalprotrusion 605 can vary based on the size of the measurement site,whether the patient is an adult or child, and so on. In addition, thelength of the protrusion 605 could be about 10 mm, or about 8 mm toabout 12 mm, or smaller than 8 mm or greater than 12 mm.

In certain embodiments, the focal length (f) for the partiallycylindrical protrusion 605 can be expressed as:

${f = \frac{R}{n - 1}},$

where R is the radius of curvature of the partial cylinder 608 and n isthe index of refraction of the material used. In certain embodiments,the radius of curvature can be between about 1.5 mm and about 2 mm. Inanother embodiment, the partially cylindrical protrusion 605 can includea material, such as nBK7 glass, with an index of refraction of around1.5 at 1300 nm, which can provide focal lengths of between about 3 mmand about 4 mm.

A partially cylindrical protrusion 605 having a material with a higherindex of refraction such as nSF11 glass (e.g., n=1.75 at 1300 nm) canprovide a shorter focal length and possibly a smaller photodiode chip,but can also cause higher reflections due to the index of refractionmismatch with air. Many types of glass or plastic can be used with indexof refraction values ranging from, for example, about 1.4 to about 1.9.The index of refraction of the material of the protrusion 605 can bechosen to improve or optimize the light focusing properties of theprotrusion 605. A plastic partially cylindrical protrusion 605 couldprovide the cheapest option in high volumes but can also have someundesired light absorption peaks at wavelengths higher than 1500 nm.Other focal lengths and materials having different indices of refractioncan be used for the partially cylindrical protrusion 605.

Placing a photodiode at a given distance below the partially cylindricalprotrusion 605 can facilitate capturing some or all of the lighttraveling perpendicular to the lens within the active area of thephotodiode (see FIG. 14). Different sizes of the partially cylindricalprotrusion 605 can use different sizes of photodiodes. The extension 610added onto the bottom of the partial cylinder 608 is used in certainembodiments to increase the height of the partially cylindricalprotrusion 605. In an embodiment, the added height is such that thephotodiodes are at or are approximately at the focal length of thepartially cylindrical protrusion 605. In an embodiment, the added heightprovides for greater thinning of the measurement site. In an embodiment,the added height assists in deflecting light piped through the sensor.This is because light piped around the sensor passes through the sidewalls of the added height without being directed toward the detectors.The extension 610 can also further facilitate the protrusion 605increasing or maximizing the amount of light that is provided to thedetectors. In some embodiments, the extension 610 can be omitted.

FIG. 6E illustrates another view of the sensor 301 f of FIG. 3F, whichincludes an embodiment of a partially cylindrical protrusion 605 b. Likethe sensor 301A shown in FIGS. 3B and 3C, the sensor 301 f includes afinger bed 310 f. The finger bed 310 f includes a generally curvedsurface shaped generally to receive tissue, such as a human digit. Thefinger bed 310 f also includes the ridges or channels 314 describedabove with respect to FIGS. 3B and 3C.

The example of finger bed 310 f shown also includes the protrusion 605b, which includes the features of the protrusion 605 described above. Inaddition, the protrusion 605 b also includes chamfered edges 607 on eachend to provide a more comfortable surface for a finger to slide across(see also FIG. 14D). In another embodiment, the protrusion 605 b couldinstead include a single chamfered edge 607 proximal to the ridges 314.In another embodiment, one or both of the chamfered edges 607 could berounded.

The protrusion 605 b also includes a measurement site contact area 670that can contact body tissue of a measurement site. The protrusion 605 bcan be removed from or integrated with the finger bed 310 f.Interchangeable, differently shaped protrusions 605 b can also beprovided, which can correspond to different finger shapes,characteristics, opacity, sizes, or the like.

FIGS. 7A and 7B illustrate block diagrams of sensors 701 that includeexample arrangements of conductive glass or conductive coated glass forshielding. Advantageously, in certain embodiments, the shielding canprovide increased SNR. The features of the sensors 701 can beimplemented with any of the sensors 101, 201, 301 described above.Although not shown, the partially cylindrical protrusion 605 of FIG. 6can also be used with the sensors 701 in certain embodiments.

For example, referring specifically to FIG. 7A, the sensor 701 aincludes an emitter housing 704 a and a detector housing 706. Theemitter housing 704 a includes LEDs 104. The detector housing 706 aincludes a tissue bed 710 a with an opening or window 703 a, theconductive glass 730 a, and one or more photodiodes for detectors 106provided on a submount 707 a.

During operation, a finger 102 can be placed on the tissue bed 710 a andoptical radiation can be emitted from the LEDs 104. Light can then beattenuated as it passes through or is reflected from the tissue of thefinger 102. The attenuated light can then pass through the opening 703 ain the tissue bed 710 a. Based on the received light, the detectors 106can provide a detector signal 107, for example, to the front endinterface 108 (see FIG. 1).

In the depicted embodiment, the conductive glass 730 is provided in theopening 703. The conductive glass 730 can thus not only permit lightfrom the finger to pass to the detectors 106, but it can also supplementthe shielding of the detectors 106 from noise. The conductive glass 730can include a stack or set of layers. In FIG. 7A, the conductive glass730 a is shown having a glass layer 731 proximate the finger 102 and aconductive layer 733 electrically coupled to the shielding 790 a.

In an embodiment, the conductive glass 730 a can be coated with aconductive, transparent or partially transparent material, such as athin film of indium tin oxide (ITO). To supplement electrical shieldingeffects of a shielding enclosure 790 a, the conductive glass 730 a canbe electrically coupled to the shielding enclosure 790 a. The conductiveglass 730 a can be electrically coupled to the shielding 704 a based ondirect contact or via other connection devices, such as a wire oranother component.

The shielding enclosure 790 a can be provided to encompass the detectors106 to reduce or prevent noise. For example, the shielding enclosure 790a can be constructed from a conductive material, such as copper, in theform of a metal cage. The shielding or enclosure a can include an opaquematerial to not only reduce electrical noise, but also ambient opticalnoise.

In some embodiments, the shielding enclosure 790 a can be constructed ina single manufactured component with or without the use of conductiveglass. This form of construction may be useful in order to reduce costsof manufacture as well as assist in quality control of the components.Furthermore, the shielding enclosure 790 a can also be used to housevarious other components, such as sigma delta components for variousembodiments of front end interfaces 108.

Referring to FIG. 7B, another block diagram of an example sensor 701 bis shown. A tissue bed 710 b of the sensor 701 b includes a protrusion705 b, which is in the form of a convex bump. The protrusion 705 b caninclude all of the features of the protrusions or tissue shapingmaterials described above. For example, the protrusion 705 b includes acontact area 307 that comes in contact with the finger 102 and which caninclude one or more openings 703 b. One or more components of conductiveglass 730 b can be provided in the openings 703. For example, in anembodiment, each of the openings 703 can include a separate window ofthe conductive glass 730 b. In an embodiment, a single piece of theconductive glass 730 b can used for some or all of the openings 703 b.The conductive glass 730 b is smaller than the conductive glass 730 a inthis particular embodiment.

A shielding enclosure 790 b is also provided, which can have all thefeatures of the shielding enclosure 790 a. The shielding enclosure 790 bis smaller than the shielding enclosure 790 a; however, a variety ofsizes can be selected for the shielding enclosures 790.

In some embodiments, the shielding enclosure 790 b can be constructed ina single manufactured component with or without the use of conductiveglass. This form of construction may be useful in order to reduce costsof manufacture as well as assist in quality control of the components.Furthermore, the shielding enclosure 790 b can also be used to housevarious other components, such as sigma delta components for variousembodiments of front end interfaces 108.

FIGS. 8A through 8D illustrate a perspective view, side views, and abottom elevation view of the conductive glass described above withrespect to the sensors 701 a, 701 b. As shown in the perspective view ofFIG. 8A and side view of FIG. 8B, the conductive glass 730 includes theelectrically conductive material 733 described above as a coating on theglass layer 731 described above to form a stack. In an embodiment wherethe electrically conductive material 733 includes indium tin oxide,surface resistivity of the electrically conductive material 733 canrange approximately from 30 ohms per square inch to 500 ohms per squareinch, or approximately 30, 200, or 500 ohms per square inch. As would beunderstood by a person of skill in the art from the present disclosure,other resistivities can also be used which are less than 30 ohms or morethan 500 ohms. Other transparent, electrically conductive materials canbe used as the material 733.

Although the conductive material 733 is shown spread over the surface ofthe glass layer 731, the conductive material 733 can be patterned orprovided on selected portions of the glass layer 731. Furthermore, theconductive material 733 can have uniform or varying thickness dependingon a desired transmission of light, a desired shielding effect, andother considerations.

In FIG. 8C, a side view of a conductive glass 830 a is shown toillustrate an embodiment where the electrically conductive material 733is provided as an internal layer between two glass layers 731, 835.Various combinations of integrating electrically conductive material 733with glass are possible. For example, the electrically conductivematerial 733 can be a layer within a stack of layers. This stack oflayers can include one or more layers of glass 731, 835, as well as oneor more layers of conductive material 733. The stack can include otherlayers of materials to achieve desired characteristics.

In FIG. 8D, a bottom perspective view is shown to illustrate anembodiment where a conductive glass 830 b can include conductivematerial 837 that occupies or covers a portion of a glass layer 839.This embodiment can be useful, for example, to create individual,shielded windows for detectors 106, such as those shown in FIG. 3C. Theconductive material 837 can be patterned to include an area 838 to allowlight to pass to detectors 106 and one or more strips 841 to couple tothe shielding 704 of FIG. 7.

Other configurations and patterns for the conductive material can beused in certain embodiments, such as, for example, a conductive coatinglining periphery edges, a conductive coating outlaid in a patternincluding a grid or other pattern, a speckled conductive coating,coating outlaid in lines in either direction or diagonally, variedthicknesses from the center out or from the periphery in, or othersuitable patterns or coatings that balance the shielding properties withtransparency considerations.

FIG. 9 depicts an example graph 900 that illustrates comparative resultsobtained by an example sensor having components similar to thosedisclosed above with respect to FIGS. 7 and 8. The graph 900 depicts theresults of the percentage of transmission of varying wavelengths oflight for different types of windows used in the sensors describedabove.

A line 915 on the graph 900 illustrates example light transmission of awindow made from plain glass. As shown, the light transmissionpercentage of varying wavelengths of light is approximately 90% for awindow made from plain glass. A line 920 on the graph 900 demonstratesan example light transmission percentage for an embodiment in which awindow is made from glass having an ITO coating with a surfaceresistivity of 500 ohms per square inch. A line 925 on the graph 900shows an example light transmission for an embodiment in which a windowis made from glass that includes a coating of ITO oxide with a surfaceresistivity of 200 ohms per square inch. A line 930 on the graph 900shows an example light transmission for an embodiment in which a windowis made from glass that includes a coating of ITO oxide with a surfaceresistivity of 30 ohms per square inch.

The light transmission percentage for a window with currently availableembedded wiring can have a light transmission percentage ofapproximately 70%. This lower percentage of light transmission can bedue to the opacity of the wiring employed in a currently availablewindow with wiring. Accordingly, certain embodiments of glass coatingsdescribed herein can employ, for example, ITO coatings with differentsurface resistivity depending on the desired light transmission,wavelengths of light used for measurement, desired shielding effect, andother criteria.

FIGS. 10A through 10B illustrate comparative noise floors of exampleimplementations of the sensors described above. Noise can includeoptical noise from ambient light and electromagnetic noise, for example,from surrounding electrical equipment. In FIG. 10A, a graph 1000 depictspossible noise floors for different frequencies of noise for anembodiment in which one of the sensors described above included separatewindows for four (4) detectors 106. One or more of the windows includedan embedded grid of wiring as a noise shield. Symbols 1030-1033illustrate the noise floor performance for this embodiment. As can beseen, the noise floor performance can vary for each of the openings andbased on the frequency of the noise.

In FIG. 10B, a graph 1050 depicts a noise floor for frequencies of noise1070 for an embodiment in which the sensor included separate openingsfor four (4) detectors 106 and one or more windows that include an ITOcoating. In this embodiment, a surface resistivity of the ITO used wasabout 500 ohms per square inch. Symbols 1080-1083 illustrate the noisefloor performance for this embodiment. As can be seen, the noise floorperformance for this embodiment can vary less for each of the openingsand provide lower noise floors in comparison to the embodiment of FIG.10A.

FIG. 11A illustrates an example structure for configuring the set ofoptical sources of the emitters described above. As shown, an emitter104 can include a driver 1105, a thermistor 1120, a set of top-emittingLEDs 1102 for emitting red and/or infrared light, a set of side-emittingLEDs 1104 for emitting near infrared light, and a submount 1106.

The thermistor 1120 can be provided to compensate for temperaturevariations. For example, the thermistor 1120 can be provided to allowfor wavelength centroid and power drift of LEDs 1102 and 1104 due toheating. In addition, other thermistors (not shown) can be employed, forexample, to measure a temperature of a measurement site. The temperaturecan be displayed on a display device and used by a caregiver. Such atemperature can also be helpful in correcting for wavelength drift dueto changes in water absorption, which can be temperature dependent,thereby providing more accurate data useful in detecting blood analyteslike glucose. In addition, using a thermistor or other type oftemperature sensitive device may be useful for detecting extremetemperatures at the measurement site that are too hot or too cold. Thepresence of low perfusion may also be detected, for example, when thefinger of a patient has become too cold. Moreover, shifts in temperatureat the measurement site can alter the absorption spectrum of water andother tissue in the measurement cite. A thermistor's temperature readingcan be used to adjust for the variations in absorption spectrum changesin the measurement site.

The driver 1105 can provide pulses of current to the emitter 1104. In anembodiment, the driver 1105 drives the emitter 1104 in a progressivefashion, for example, in an alternating manner based on a control signalfrom, for example, a processor (e.g., the processor 110). For example,the driver 1105 can drive the emitter 1104 with a series of pulses toabout 1 milliwatt (mW) for visible light to light at about 1300 nm andfrom about 40 mW to about 100 mW for light at about 1600 nm to about1700 nm. However, a wide number of driving powers and drivingmethodologies can be used. The driver 1105 can be synchronized withother parts of the sensor and can minimize or reduce any jitter in thetiming of pulses of optical radiation emitted from the emitter 1104. Insome embodiments, the driver 1105 is capable of driving the emitter 1104to emit an optical radiation in a pattern that varies by less than about10 parts-per-million; however other amounts of variation can be used.

The submount 1106 provides a support structure in certain embodimentsfor aligning the top-emitting LEDs 1102 and the side-emitting LEDs 1104so that their optical radiation is transmitted generally towards themeasurement site. In some embodiments, the submount 1106 is alsoconstructed of aluminum nitride (AlN) or beryllium oxide (BEO) for heatdissipation, although other materials or combinations of materialssuitable for the submount 1106 can be used.

FIG. 11B illustrates a configuration of emitting optical radiation intoa measurement site for measuring a blood constituent or analyte likeglucose. In some embodiments, emitter 104 may be driven in a progressivefashion to minimize noise and increase SNR of sensor 101. For example,emitter 104 may be driven based on a progression of power/currentdelivered to LEDs 1102 and 1104.

In some embodiments, emitter 104 may be configured to emit pulsescentered about 905 nm, about 1050 nm, about 1200 nm, about 1300 nm,about 1330 nm, about 1610 nm, about 1640 nm, and about 1665 nm. Inanother embodiment, the emitter 104 may emit optical radiation rangingfrom about 860 nm to about 950 nm, about 950 nm to about 1100 nm, about1100 nm to about 1270 nm, about 1250 nm to about 1350 nm, about 1300 nmto about 1360 nm, and about 1590 nm to about 1700 nm. Of course, emitter104 may be configured to transmit any of a variety of wavelengths ofvisible, or near-infrared optical radiation.

For purposes of illustration, FIG. 11B shows a sequence of pulses oflight at wavelengths of around 905 nm, around 1200 nm, around 1300 nm,and around 1330 nm from top emitting LEDs 1102. FIG. 11B also shows thatemitter 104 may then emit pulses centered at around 1630 nm, around 1660nm, and around 1615 nm from side emitting LEDs 1104. Emitter 104 may beprogressively driven at higher power/current. This progression may allowdriver circuit 105 to stabilize in its operations, and thus, provide amore stable current/power to LEDs 1102 and 1104.

For example, as shown in FIG. 11B, the sequence of optical radiationpulses are shown having a logarithmic-like progression in power/current.In some embodiments, the timing of these pulses is based on a cycle ofabout 400 slots running at 48 kHz (e.g. each time slot may beapproximately 0.02 ms or 20 microseconds). An artisan will recognizethat term “slots” includes its ordinary meaning, which includes a timeperiod that may also be expressed in terms of a frequency. In theexample shown, pulses from top emitting LEDs 1102 may have a pulse widthof about 40 time slots (e.g., about 0.8 ms) and an off period of about 4time slots in between. In addition, pulses from side emitting LEDs 1104(e.g., or a laser diode) may have a pulse width of about 60 time slots(e.g., about 1.25 ms) and a similar off period of about 4 time slots. Apause of about 70 time slots (e.g. 1.5 ms) may also be provided in orderto allow driver circuit 1105 to stabilize after operating at highercurrent/power.

As shown in FIG. 11B, top emitting LEDs 1102 may be initially drivenwith a power to approximately 1 mW at a current of about 20-100 mA.Power in these LEDs may also be modulated by using a filter or coveringof black dye to reduce power output of LEDs. In this example, topemitting LEDs 1102 may be driven at approximately 0.02 to 0.08 mW. Thesequence of the wavelengths may be based on the current requirements oftop emitting LEDs 502 for that particular wavelength. Of course, inother embodiments, different wavelengths and sequences of wavelengthsmay be output from emitter 104.

Subsequently, side emitting LEDs 1104 may be driven at higher powers,such as about 40-100 mW and higher currents of about 600-800 mA. Thishigher power may be employed in order to compensate for the higheropacity of tissue and water in measurement site 102 to thesewavelengths. For example, as shown, pulses at about 1630 nm, about 1660nm, and about 1615 nm may be output with progressively higher power,such as at about 40 mW, about 50 mW, and about 60 mW, respectively. Inthis embodiment, the order of wavelengths may be based on the opticalcharacteristics of that wavelength in tissue as well as the currentneeded to drive side emitting LEDs 1104. For example, in thisembodiment, the optical pulse at about 1615 nm is driven at the highestpower due to its sensitivity in detecting analytes like glucose and theability of light at this wavelength to penetrate tissue. Of course,different wavelengths and sequences of wavelengths may be output fromemitter 104.

As noted, this progression may be useful in some embodiments because itallows the circuitry of driver circuit 1105 to stabilize its powerdelivery to LEDs 1102 and 1104. Driver circuit 1105 may be allowed tostabilize based on the duty cycle of the pulses or, for example, byconfiguring a variable waiting period to allow for stabilization ofdriver circuit 1105. Of course, other variations in power/current andwavelength may also be employed in the present disclosure.

Modulation in the duty cycle of the individual pulses may also be usefulbecause duty cycle can affect the signal noise ratio of the system 100.That is, as the duty cycle is increased so may the signal to noiseratio.

Furthermore, as noted above, driver circuit 1105 may monitortemperatures of the LEDs 1102 and 1104 using the thermistor 1120 andadjust the output of LEDs 1102 and 1104 accordingly. Such a temperaturemay be to help sensor 101 correct for wavelength drift due to changes inwater absorption, which can be temperature dependent.

FIG. 11C illustrates another exemplary emitter that may be employed inthe sensor according to an embodiment of the disclosure. As shown, theemitter 104 can include components mounted on a substrate 1108 and onsubmount 1106. In particular, top-emitting LEDs 1102 for emitting redand/or infrared light may be mounted on substrate 1108. Side emittingLEDS 1104 may be mounted on submount 1106. As noted, side-emitting LEDs1104 may be included in emitter 104 for emitting near infrared light.

As also shown, the sensor of FIG. 11C may include a thermistor 1120. Asnoted, the thermistor 1120 can be provided to compensate for temperaturevariations. The thermistor 1120 can be provided to allow for wavelengthcentroid and power drift of LEDs 1102 and 1104 due to heating. Inaddition, other thermistors (not shown) can be employed, for example, tomeasure a temperature of a measurement site. Such a temperature can behelpful in correcting for wavelength drift due to changes in waterabsorption, which can be temperature dependent, thereby providing moreaccurate data useful in detecting blood analytes like glucose.

In some embodiments, the emitter 104 may be implemented without the useof side emitting LEDs. For example, certain blood constituents, such astotal hemoglobin, can be measured by embodiments of the disclosurewithout the use of side emitting LEDs. FIG. 11D illustrates anotherexemplary emitter that may be employed in the sensor according to anembodiment of the disclosure. In particular, an emitter 104 that isconfigured for a blood constituent, such as total hemoglobin, is shown.The emitter 104 can include components mounted on a substrate 1108. Inparticular, top-emitting LEDs 1102 for emitting red and/or infraredlight may be mounted on substrate 1108.

As also shown, the emitter of FIG. 11D may include a thermistor 1120.The thermistor 1120 can be provided to compensate for temperaturevariations. The thermistor 1120 can be provided to allow for wavelengthcentroid and power drift of LEDs 1102 due to heating.

FIG. 12A illustrates a detector submount 1200 having photodiodedetectors that are arranged in a grid pattern on the detector submount1200 to capture light at different quadrants from a measurement site.One detector submount 1200 can be placed under each window of thesensors described above, or multiple windows can be placed over a singledetector submount 1200. The detector submount 1200 can also be used withthe partially cylindrical protrusion 605 described above with respect toFIG. 6.

The detectors include photodiode detectors 1-4 that are arranged in agrid pattern on the submount 1200 to capture light at differentquadrants from the measurement site. As noted, other patterns ofphotodiodes, such as a linear row, or logarithmic row, can also beemployed in certain embodiments.

As shown, the detectors 1-4 may have a predetermined spacing from eachother, or spatial relationship among one another that result in aspatial configuration. This spatial configuration can be configured topurposefully create a variation of path lengths among detectors 106 andthe point light source discussed above.

Detectors may hold multiple (e.g., two, three, four, etc.) photodiodearrays that are arranged in a two-dimensional grid pattern. Multiplephotodiode arrays may also be useful to detect light piping (i.e., lightthat bypasses measurement site 102). As shown, walls may separate theindividual photodiode arrays to prevent mixing of light signals fromdistinct quadrants. In addition, as noted, the detectors may be coveredby windows of transparent material, such as glass, plastic, etc., toallow maximum transmission of power light captured. As noted, thiswindow may comprise some shielding in the form of an embedded grid ofwiring, or a conductive layer or coating.

FIGS. 12B through 12D illustrate a simplified view of exemplaryarrangements and spatial configurations of photodiodes for detectors106. As shown, detectors 106 may comprise photodiode detectors 1-4 thatare arranged in a grid pattern on detector submount 1200 to capturelight at different quadrants from measurement site 102.

As noted, other patterns of photodiodes may also be employed inembodiments of the present disclosure, including, for example, stackedor other configurations recognizable to an artisan from the disclosureherein. For example, detectors 106 may be arranged in a linear array, alogarithmic array, a two-dimensional array, and the like. Furthermore,an artisan will recognize from the disclosure herein that any number ofdetectors 106 may be employed by embodiments of the present disclosure.

For example, as shown in FIG. 12B, detectors 106 may comprise photodiodedetectors 1-4 that are arranged in a substantially linear configurationon submount 1200. In this embodiment shown, photodiode detectors 1-4 aresubstantially equally spaced apart (e.g., where the distance D issubstantially the same between detectors 1-4).

In FIG. 12C, photodiode detectors 1-4 may be arranged in a substantiallylinear configuration on submount 1200, but may employ a substantiallyprogressive, substantially logarithmic, or substantiallysemi-logarithmic spacing (e.g., where distances D1>D2>D3). Thisarrangement or pattern may be useful for use on a patient's finger andwhere the thickness of the finger gradually increases.

In FIG. 12D, a different substantially grid pattern on submount 1200 ofphotodiode detectors 1-4 is shown. As noted, other patterns of detectorsmay also be employed in embodiments of the present invention.

FIGS. 12E through 12H illustrate several embodiments of photodiodes thatmay be used in detectors 106. As shown in these figures, a photodiode1202 of detector 106 may comprise a plurality of active areas 1204,These active areas 204 may be coupled together via a common cathode 1206or anode 1208 in order to provide a larger effective detection area.

In particular, as shown in FIG. 12E, photodiode 1202 may comprise two(2) active areas 1204 a and 1204 b. In FIG. 12F, photodiode 1202 maycomprise four (4) active areas 1204 c-f. In FIG. 12G, photodiode 1202may comprise three (3) active areas 1204 g-i. In FIG. 12H, photodiode1202 may comprise nine (9) active areas 1204 j-r. The use of smalleractive areas may be useful because smaller active areas can be easier tofabricate and can be fabricated with higher purity. However, one skilledin the art will recognize that various sizes of active areas may beemployed in the photodiode 1202.

FIG. 13 illustrates an example multi-stream process 1300. Themulti-stream process 1300 can be implemented by the data collectionsystem 100 and/or by any of the sensors described above. As shown, acontrol signal from a signal processor 1310 controls a driver 1305. Inresponse, an emitter 1304 generates a pulse sequence 1303 from itsemitter (e.g., its LEDs) into a measurement site or sites 1302. Asdescribed above, in some embodiments, the pulse sequence 1303 iscontrolled to have a variation of about 10 parts per million or less. Ofcourse, depending on the analyte desired, the tolerated variation in thepulse sequence 1303 can be greater (or smaller).

In response to the pulse sequence 1300, detectors 1 to n (n being aninteger) in a detector 1306 capture optical radiation from themeasurement site 1302 and provide respective streams of output signals.Each signal from one of detectors 1-n can be considered a stream havingrespective time slots corresponding to the optical pulses from emittersets 1-n in the emitter 1304. Although n emitters and n detectors areshown, the number of emitters and detectors need not be the same incertain implementations.

A front end interface 1308 can accept these multiple streams fromdetectors 1-n and deliver one or more signals or composite signal(s)back to the signal processor 1310. A stream from the detectors 1-n canthus include measured light intensities corresponding to the lightpulses emitted from the emitter 1304.

The signal processor 1310 can then perform various calculations tomeasure the amount of glucose and other analytes based on these multiplestreams of signals. In order to help explain how the signal processor1310 can measure analytes like glucose, a primer on the spectroscopyemployed in these embodiments will now be provided.

Spectroscopy is premised upon the Beer-Lambert law. According to thislaw, the properties of a material, e.g., glucose present in ameasurement site, can be deterministically calculated from theabsorption of light traveling through the material. Specifically, thereis a logarithmic relation between the transmission of light through amaterial and the concentration of a substance and also between thetransmission and the length of the path traveled by the light. As noted,this relation is known as the Beer-Lambert law.

The Beer-Lambert law is usually written as:

Absorbance A=m*b*c, where:

m is the wavelength-dependent molar absorptivity coefficient (usuallyexpressed in units of M⁻¹ cm⁻¹);

b is the mean path length; and

c is the analyte concentration (e.g., the desired parameter).

In spectroscopy, instruments attempt to obtain the analyte concentration(c) by relating absorbance (A) to transmittance (T). Transmittance is aproportional value defined as:

T=I/I _(o), where:

I is the light intensity measured by the instrument from the measurementsite; and

I_(o) is the initial light intensity from the emitter.

Absorbance (A) can be equated to the transmittance (T) by the equation:

A=−log T

Therefore, substituting equations from above:

A=−log(I/I _(o))

In view of this relationship, spectroscopy thus relies on aproportional-based calculation of −log(I/I_(o)) and solving for analyteconcentration (c).

Typically, in order to simplify the calculations, spectroscopy will usedetectors that are at the same location in order to keep the path length(b) a fixed, known constant. In addition, spectroscopy will employvarious mechanisms to definitively know the transmission power (I_(o)),such as a photodiode located at the light source. This architecture canbe viewed as a single channel or single stream sensor, because thedetectors are at a single location.

However, this scheme can encounter several difficulties in measuringanalytes, such as glucose. This can be due to the high overlap ofabsorption of light by water at the wavelengths relevant to glucose aswell as other factors, such as high self-noise of the components.

Embodiments of the present disclosure can employ a different approachthat in part allows for the measurement of analytes like glucose. Someembodiments can employ a bulk, non-pulsatile measurement in order toconfirm or validate a pulsatile measurement. In addition, both thenon-pulsatile and pulsatile measurements can employ, among other things,the multi-stream operation described above in order to attain sufficientSNR. In particular, a single light source having multiple emitters canbe used to transmit light to multiple detectors having a spatialconfiguration.

A single light source having multiple emitters can allow for a range ofwavelengths of light to be used. For example, visible, infrared, andnear infrared wavelengths can be employed. Varying powers of lightintensity for different wavelengths can also be employed.

Secondly, the use of multiple-detectors in a spatial configuration allowfor a bulk measurement to confirm or validate that the sensor ispositioned correctly. This is because the multiple locations of thespatial configuration can provide, for example, topology informationthat indicates where the sensor has been positioned. Currently availablesensors do not provide such information. For example, if the bulkmeasurement is within a predetermined range of values, then this canindicate that the sensor is positioned correctly in order to performpulsatile measurements for analytes like glucose. If the bulkmeasurement is outside of a certain range or is an unexpected value,then this can indicate that the sensor should be adjusted, or that thepulsatile measurements can be processed differently to compensate, suchas using a different calibration curve or adjusting a calibration curve.This feature and others allow the embodiments to achieve noisecancellation and noise reduction, which can be several times greater inmagnitude that what is achievable by currently available technology.

In order to help illustrate aspects of the multi-stream measurementapproach, the following example derivation is provided. Transmittance(T) can be expressed as:

T=e ^(−m*b*c)

In terms of light intensity, this equation can also be rewritten as:

I/I _(o) =e ^(−m*b*c)

Or, at a detector, the measured light (I) can be expressed as:

I=I _(o) *e ^(−m*b*c)

As noted, in the present disclosure, multiple detectors (1 to n) can beemployed, which results in I₁ . . . I_(n) In streams of measurements.Assuming each of these detectors have their own path lengths, b₁ . . .b_(n), from the light source, the measured light intensities can beexpressed as:

I _(n) =I _(o) *e ^(−m*b) ^(n) ^(*c)

The measured light intensities at any two different detectors can bereferenced to each other. For example:

I ₁ I _(n)=(I _(o) *e ^(−mb) ¹ ^(c))/(I _(o) *e ^(−mb) ^(n) ^(c))

As can be seen, the terms, I_(o), cancel out and, based on exponentalgebra, the equation can be rewritten as:

I ₁ /I _(n) =e ^(−m(b) ¹ ^(−b) ^(n) ^()c)

From this equation, the analyte concentration (c) can now be derivedfrom bulk signals I₁ . . . I_(n) and knowing the respective mean pathlengths b₁ and b_(n). This scheme also allows for the cancelling out ofI_(o), and thus, noise generated by the emitter 1304 can be cancelledout or reduced. In addition, since the scheme employs a mean path lengthdifference, any changes in mean path length and topological variationsfrom patient to patient are easily accounted. Furthermore, thisbulk-measurement scheme can be extended across multiple wavelengths.This flexibility and other features allow embodiments of the presentdisclosure to measure blood analytes like glucose.

For example, as noted, the non-pulsatile, bulk measurements can becombined with pulsatile measurements to more accurately measure analyteslike glucose. In particular, the non-pulsatile, bulk measurement can beused to confirm or validate the amount of glucose, protein, etc. in thepulsatile measurements taken at the tissue at the measurement site(s)1302. The pulsatile measurements can be used to measure the amount ofglucose, hemoglobin, or the like that is present in the blood.Accordingly, these different measurements can be combined to thusdetermine analytes like blood glucose.

FIG. 14A illustrates an embodiment of a detector submount 1400 apositioned beneath the partially cylindrical protrusion 605 of FIG. 6(or alternatively, the protrusion 605 b). The detector submount 1400 aincludes two rows 1408 a of detectors 1410 a. The partially cylindricalprotrusion 605 can facilitate reducing the number and/or size ofdetectors used in a sensor because the protrusion 605 can act as a lensthat focuses light onto a smaller area.

To illustrate, in some sensors that do not include the partiallycylindrical protrusion 605, sixteen detectors can be used, includingfour rows of four detectors each. Multiple rows of detectors can be usedto measure certain analytes, such as glucose or total hemoglobin, amongothers. Multiple rows of detectors can also be used to detect lightpiping (e.g., light that bypasses the measurement site). However, usingmore detectors in a sensor can add cost, complexity, and noise to thesensor.

Applying the partially cylindrical protrusion 605 to such a sensor,however, could reduce the number of detectors or rows of detectors usedwhile still receiving the substantially same amount of light, due to thefocusing properties of the protrusion 605 (see FIG. 14B). This is theexample situation illustrated in FIG. 14—two rows 1408 a of detectors1410 a are used instead of four. Advantageously, in certain embodiments,the resulting sensor can be more cost effective, have less complexity,and have an improved SNR, due to fewer and/or smaller photodiodes.

In other embodiments, using the partially cylindrical protrusion 605 canallow the number of detector rows to be reduced to one or three rows offour detectors. The number of detectors in each row can also be reduced.Alternatively, the number of rows might not be reduced but the size ofthe detectors can be reduced. Many other configurations of detector rowsand sizes can also be provided.

FIG. 14B depicts a front elevation view of the partially cylindricalprotrusion 605 (or alternatively, the protrusion 605 b) that illustrateshow light from emitters (not shown) can be focused by the protrusion 605onto detectors. The protrusion 605 is placed above a detector submount1400 b having one or more detectors 1410 b disposed thereon. Thesubmount 1400 b can include any number of rows of detectors 1410,although one row is shown.

Light, represented by rays 1420, is emitted from the emitters onto theprotrusion 605. These light rays 1420 can be attenuated by body tissue(not shown). When the light rays 1420 enter the protrusion 605, theprotrusion 605 acts as a lens to refract the rays into rays 1422. Thisrefraction is caused in certain embodiments by the partially cylindricalshape of the protrusion 605. The refraction causes the rays 1422 to befocused or substantially focused on the one or more detectors 1410 b.Since the light is focused on a smaller area, a sensor including theprotrusion 605 can include fewer detectors to capture the same amount oflight compared with other sensors.

FIG. 14C illustrates another embodiment of a detector submount 1400 c,which can be disposed under the protrusion 605 b (or alternatively, theprotrusion 605). The detector submount 1400 c includes a single row 1408c of detectors 1410 c. The detectors are electrically connected toconductors 1412 c, which can be gold, silver, copper, or any othersuitable conductive material.

The detector submount 1400 c is shown positioned under the protrusion605 b in a detector subassembly 1450 illustrated in FIG. 14D. A top-downview of the detector subassembly 1450 is also shown in FIG. 14E. In thedetector subassembly 1450, a cylindrical housing 1430 is disposed on thesubmount 1400 c. The cylindrical housing 1430 includes a transparentcover 1432, upon which the protrusion 605 b is disposed. Thus, as shownin FIG. 14D, a gap 1434 exists between the detectors 1410 c and theprotrusion 605 b. The height of this gap 1434 can be chosen to increaseor maximize the amount of light that impinges on the detectors 1410 c.

The cylindrical housing 1430 can be made of metal, plastic, or anothersuitable material. The transparent cover 1432 can be fabricated fromglass or plastic, among other materials. The cylindrical housing 1430can be attached to the submount 1400 c at the same time or substantiallythe same time as the detectors 1410 c to reduce manufacturing costs. Ashape other than a cylinder can be selected for the housing 1430 invarious embodiments.

In certain embodiments, the cylindrical housing 1430 (and transparentcover 1432) forms an airtight or substantially airtight or hermetic sealwith the submount 1400 c. As a result, the cylindrical housing 1430 canprotect the detectors 1410 c and conductors 1412 c from fluids andvapors that can cause corrosion. Advantageously, in certain embodiments,the cylindrical housing 1430 can protect the detectors 1410 c andconductors 1412 c more effectively than currently-available resinepoxies, which are sometimes applied to solder joints between conductorsand detectors.

In embodiments where the cylindrical housing 1430 is at least partiallymade of metal, the cylindrical housing 1430 can provide noise shieldingfor the detectors 1410 c. For example, the cylindrical housing 1430 canbe soldered to a ground connection or ground plane on the submount 1400c, which allows the cylindrical housing 1430 to reduce noise. In anotherembodiment, the transparent cover 1432 can include a conductive materialor conductive layer, such as conductive glass or plastic. Thetransparent cover 1432 can include any of the features of the noiseshields 790 described above.

The protrusion 605 b includes the chamfered edges 607 described abovewith respect to FIG. 6E. These chamfered edges 607 can allow a patientto more comfortably slide a finger over the protrusion 605 b wheninserting the finger into the sensor 301 f.

FIG. 14F illustrates a portion of the detector shell 306 f, whichincludes the detectors 1410 c on the substrate 1400 c. The substrate1400 c is enclosed by a shielding enclosure 1490, which can include thefeatures of the shielding enclosures 790 a, 790 b described above (seealso FIG. 17). The shielding enclosure 1490 can be made of metal. Theshielding enclosure 1490 includes a window 1492 a above the detectors1410 c, which allows light to be transmitted onto the detectors 1410 c.

A noise shield 1403 is disposed above the shielding enclosure 1490. Thenoise shield 1403, in the depicted embodiment, includes a window 1492 acorresponding to the window 1492 a. Each of the windows 1492 a, 1492 bcan include glass, plastic, or can be an opening without glass orplastic. In some embodiments, the windows 1492 a, 1492 b may be selectedto have different sizes or shapes from each other.

The noise shield 1403 can include any of the features of the conductiveglass described above. In the depicted embodiment, the noise shield 1403extends about three-quarters of the length of the detector shell 306 f.In other embodiments, the noise shield 1403 could be smaller or larger.The noise shield 1403 could, for instance, merely cover the detectors1410 c, the submount 1400 c, or a portion thereof. The noise shield 1403also includes a stop 1413 for positioning a measurement site within thesensor 301 f. Advantageously, in certain embodiments, the noise shield1403 can reduce noise caused by light piping.

A thermistor 1470 is also shown. The thermistor 1470 is attached to thesubmount 1400 c and protrudes above the noise shield 1403. As describedabove, the thermistor 1470 can be employed to measure a temperature of ameasurement site. Such a temperature can be helpful in correcting forwavelength drift due to changes in water absorption, which can betemperature dependent, thereby providing more accurate data useful indetecting blood analytes like glucose.

In the depicted embodiment, the detectors 1410 c are not enclosed in thecylindrical housing 1430. In an alternative embodiment, the cylindricalhousing 1430 encloses the detectors 1410 c and is disposed under thenoise shield 1403. In another embodiment, the cylindrical housing 1430encloses the detectors 1410 c and the noise shield 1403 is not used. Ifboth the cylindrical housing 1403 and the noise shield 1403 are used,either or both can have noise shielding features.

FIG. 14G illustrates the detector shell 306 f of FIG. 14F, with thefinger bed 310 f disposed thereon. FIG. 14H illustrates the detectorshell 306 f of FIG. 14G, with the protrusion 605 b disposed in thefinger bed 310 f.

FIG. 14I illustrates a cutaway view of the sensor 301 f. Not allfeatures of the sensor 301 f are shown, such as the protrusion 605 b.Features shown include the emitter and detector shells 304 f, 306 f, theflaps 307 f, the heat sink 350 f and fins 351 f, the finger bed 310 f,and the noise shield 1403.

In addition to these features, emitters 1404 are depicted in the emittershell 304 f. The emitters 1404 are disposed on a submount 1401, which isconnected to a circuit board 1419. The emitters 1404 are also enclosedwithin a cylindrical housing 1480. The cylindrical housing 1480 caninclude all of the features of the cylindrical housing 1430 describedabove. For example, the cylindrical housing 1480 can be made of metal,can be connected to a ground plane of the submount 1401 to provide noiseshielding, and can include a transparent cover 1482.

The cylindrical housing 1480 can also protect the emitters 1404 fromfluids and vapors that can cause corrosion. Moreover, the cylindricalhousing 1480 can provide a gap between the emitters 1404 and themeasurement site (not shown), which can allow light from the emitters1404 to even out or average out before reaching the measurement site.

The heat sink 350 f, in addition to including the fins 351 f, includes aprotuberance 352 f that extends down from the fins 351 f and contactsthe submount 1401. The protuberance 352 f can be connected to thesubmount 1401, for example, with thermal paste or the like. Theprotuberance 352 f can sink heat from the emitters 1404 and dissipatethe heat via the fins 351 f.

FIGS. 15A and 15B illustrate embodiments of sensor portions 1500A, 1500Bthat include alternative heat sink features to those described above.These features can be incorporated into any of the sensors describedabove. For example, any of the sensors above can be modified to use theheat sink features described below instead of or in addition to the heatsink features of the sensors described above.

The sensor portions 1500A, 1500B shown include LED emitters 1504;however, for ease of illustration, the detectors have been omitted. Thesensor portions 1500A, 1500B shown can be included, for example, in anyof the emitter shells described above.

The LEDs 1504 of the sensor portions 1500A, 1500B are connected to asubstrate or submount 1502. The submount 1502 can be used in place ofany of the submounts described above. The submount 1502 can be anon-electrically conducting material made of any of a variety ofmaterials, such as ceramic, glass, or the like. A cable 1512 is attachedto the submount 1502 and includes electrical wiring 1514, such astwisted wires and the like, for communicating with the LEDs 1504. Thecable 1512 can correspond to the cables 212 described above.

Although not shown, the cable 1512 can also include electricalconnections to a detector. Only a portion of the cable 1512 is shown forclarity. The depicted embodiment of the cable 1512 includes an outerjacket 1510 and a conductive shield 1506 disposed within the outerjacket 1510. The conductive shield 1506 can be a ground shield or thelike that is made of a metal such as braided copper or aluminum. Theconductive shield 1506 or a portion of the conductive shield 1506 can beelectrically connected to the submount 1502 and can reduce noise in thesignal generated by the sensor 1500A, 1500B by reducing RF coupling withthe wires 1514. In alternative embodiments, the cable 1512 does not havea conductive shield. For example, the cable 1512 could be a twisted paircable or the like, with one wire of the twisted pair used as a heatsink.

Referring specifically to FIG. 15A, in certain embodiments, theconductive shield 1506 can act as a heat sink for the LEDs 1504 byabsorbing thermal energy from the LEDs 1504 and/or the submount 1502. Anoptional heat insulator 1520 in communication with the submount 1502 canalso assist with directing heat toward the conductive shield 1506. Theheat insulator 1520 can be made of plastic or another suitable material.Advantageously, using the conductive shield 1506 in the cable 1512 as aheat sink can, in certain embodiments, reduce cost for the sensor.

Referring to FIG. 15B, the conductive shield 1506 can be attached toboth the submount 1502 and to a heat sink layer 1530 sandwiched betweenthe submount 1502 and the optional insulator 1520. Together, the heatsink layer 1530 and the conductive shield 1506 in the cable 1512 canabsorb at least part of the thermal energy from the LEDs and/or thesubmount 1502.

FIGS. 15C and 15D illustrate implementations of a sensor portion 1500Cthat includes the heat sink features of the sensor portion 1500Adescribed above with respect to FIG. 15A. The sensor portion 1500Cincludes the features of the sensor portion 1500A, except that theoptional insulator 1520 is not shown. FIG. 15D is a side cutaway view ofthe sensor portion 1500C that shows the emitters 1504.

The cable 1512 includes the outer jacket 1510 and the conductive shield1506. The conductive shield 1506 is soldered to the submount 1502, andthe solder joint 1561 is shown. In some embodiments, a larger solderjoint 1561 can assist with removing heat more rapidly from the emitters1504. Various connections 1563 between the submount 1502 and a circuitboard 1519 are shown. In addition, a cylindrical housing 1580,corresponding to the cylindrical housing 1480 of FIG. 14I, is shownprotruding through the circuit board 1519. The emitters 1504 areenclosed in the cylindrical housing 1580.

FIGS. 15E and 15F illustrate implementations of a sensor portion 1500Ethat includes the heat sink features of the sensor portion 1500Bdescribed above with respect to FIG. 15B. The sensor portion 1500Eincludes the heat sink layer 1530. The heat sink layer 1530 can be ametal plate, such as a copper plate or the like. The optional insulator1520 is not shown. FIG. 15F is a side cutaway view of the sensor portion1500E that shows the emitters 1504.

In the depicted embodiment, the conductive shield 1506 of the cable 1512is soldered to the heat sink layer 1530 instead of the submount 1502.The solder joint 1565 is shown. In some embodiments, a larger solderjoint 1565 can assist with removing heat more rapidly from the emitters1504. Various connections 1563 between the submount 1502 and a circuitboard 1519 are shown. In addition, the cylindrical housing 1580 is shownprotruding through the circuit board 1519. The emitters 1504 areenclosed in the cylindrical housing 1580.

FIGS. 15G and 15H illustrate embodiments of connector features that canbe used with any of the sensors described above with respect to FIGS. 1through 15F. Referring to FIG. 15G, the circuit board 1519 includes afemale connector 1575 that mates with a male connector 1577 connected toa daughter board 1587. The daughter board 1587 includes connections tothe electrical wiring 1514 of the cable 1512. The connected boards 1519,1587 are shown in FIG. 15H. Also shown is a hole 1573 that can receivethe cylindrical housing 1580 described above.

Advantageously, in certain embodiments, using a daughter board 1587 toconnect to the circuit board 1519 can enable connections to be made moreeasily to the circuit board 1519. In addition, using separate boards canbe easier to manufacture than a single circuit board 1519 with allconnections soldered to the circuit board 1519.

FIG. 15I illustrates an exemplary architecture for front-end interface108 as a transimpedance-based front-end. As noted, front-end interfaces108 provide an interface that adapts the output of detectors 106 into aform that can be handled by signal processor 110. As shown in thisfigure, sensor 101 and front-end interfaces 108 may be integratedtogether as a single component, such as an integrated circuit. Ofcourse, one skilled in the art will recognize that sensor 101 and frontend interfaces 108 may comprise multiple components or circuits that arecoupled together.

Front-end interfaces 108 may be implemented using transimpedanceamplifiers that are coupled to analog to digital converters in a sigmadelta converter. In some embodiments, a programmable gain amplifier(PGA) can be used in combination with the transimpedance-basedfront-ends. For example, the output of a transimpedance-based front-endmay be output to a sigma-delta ADC that comprises a PGA. A PGA may beuseful in order to provide another level of amplification and control ofthe stream of signals from detectors 106. The PGA may be an integratedcircuit or built from a set of micro-relays. Alternatively, the PGA andADC components in converter 900 may be integrated with thetransimpedance-based front-end in sensor 101.

Due to the low-noise requirements for measuring blood analytes likeglucose and the challenge of using multiple photodiodes in detector 106,the applicants developed a noise model to assist in configuringfront-end 108. Conventionally, those skilled in the art have focused onoptimizing the impedance of the transimpedance amplifiers to minimizenoise.

However, the following noise model was discovered by the applicants:

Noise=√{square root over (aR+bR ²)}, where:

aR is characteristic of the impedance of the transimpedance amplifier;and

bR² is characteristic of the impedance of the photodiodes in detectorand the number of photodiodes in detector 106.

The foregoing noise model was found to be helpful at least in part dueto the high SNR required to measure analytes like glucose. However, theforegoing noise model was not previously recognized by artisans at leastin part because, in conventional devices, the major contributor to noisewas generally believed to originate from the emitter or the LEDs.Therefore, artisans have generally continued to focus on reducing noiseat the emitter.

However, for analytes like glucose, the discovered noise model revealedthat one of the major contributors to noise was generated by thephotodiodes. In addition, the amount of noise varied based on the numberof photodiodes coupled to a transimpedance amplifier. Accordingly,combinations of various photodiodes from different manufacturers,different impedance values with the transimpedance amplifiers, anddifferent numbers of photodiodes were tested as possible embodiments.

In some embodiments, different combinations of transimpedance tophotodiodes may be used. For example, detectors 1-4 (as shown, e.g., inFIG. 12A) may each comprise four photodiodes. In some embodiments, eachdetector of four photodiodes may be coupled to one or moretransimpedance amplifiers. The configuration of these amplifiers may beset according to the model shown in FIG. 15J.

Alternatively, each of the photodiodes may be coupled to its ownrespective transimpedance amplifier. For example, transimpedanceamplifiers may be implemented as integrated circuits on the same circuitboard as detectors 1-4. In this embodiment, the transimpedanceamplifiers may be grouped into an averaging (or summing) circuit, whichare known to those skilled in the art, in order to provide an outputstream from the detector. The use of a summing amplifier to combineoutputs from several transimpedance amplifiers into a single, analogsignal may be helpful in improving the SNR relative to what isobtainable from a single transimpedance amplifier. The configuration ofthe transimpedance amplifiers in this setting may also be set accordingto the model shown in FIG. 15J.

As yet another alternative, as noted above with respect to FIGS. 12Ethrough 12H, the photodiodes in detectors 106 may comprise multipleactive areas that are grouped together. In some embodiments, each ofthese active areas may be provided its own respective transimpedance.This form of pairing may allow a transimpedance amplifier to be bettermatched to the characteristics of its corresponding photodiode or activearea of a photodiode.

As noted, FIG. 15J illustrates an exemplary noise model that may beuseful in configuring transimpedance amplifiers. As shown, for a givennumber of photodiodes and a desired SNR, an optimal impedance value fora transimpedance amplifier could be determined.

For example, an exemplary “4 PD per stream” sensor 1502 is shown wheredetector 106 comprises four photodiodes 1502. The photodiodes 1502 arecoupled to a single transimpedance amplifier 1504 to produce an outputstream 1506. In this example, the transimpedance amplifier comprises 10MΩ resistors 1508 and 1510. Thus, output stream 1506 is produced fromthe four photodiodes (PD) 1502. As shown in the graph of FIG. 15J, themodel indicates that resistance values of about 10 MΩ may provide anacceptable SNR for analytes like glucose.

However, as a comparison, an exemplary “1 PD per stream” sensor 1512 isalso shown in FIG. 15J. In particular, sensor 1512 may comprise aplurality of detectors 106 that each comprises a single photodiode 1514.In addition, as shown for this example configuration, each ofphotodiodes 1514 may be coupled to respective transimpedance amplifiers1516, e.g., 1 PD per stream. Transimpedance amplifiers are shown having40 MΩ resistors 1518. As also shown in the graph of FIG. 15J, the modelillustrates that resistance values of 40 MΩ for resistors 1518 may serveas an alternative to the 4 photodiode per stream architecture of sensor1502 described above and yet still provide an equivalent SNR.

Moreover, the discovered noise model also indicates that utilizing a 1photodiode per stream architecture like that in sensor 1512 may provideenhanced performance because each of transimpedance amplifiers 1516 canbe tuned or optimized to its respective photodiodes 1518. In someembodiments, an averaging component 1520 may also be used to help cancelor reduce noise across photodiodes 1518.

For purposes of illustration, FIG. 15K shows different architectures(e.g., four PD per stream and one PD per stream) for various embodimentsof a sensor and how components of the sensor may be laid out on acircuit board or substrate. For example, sensor 1522 may comprise a “4PD per stream” architecture on a submount 700 in which each detector 106comprises four (4) photodiodes 1524. As shown for sensor 1522, theoutput of each set of four photodiodes 1524 is then aggregated into asingle transimpedance amplifier 1526 to produce a signal.

As another example, a sensor 1528 may comprise a “1 PD per stream”architecture on submount 700 in which each detector 106 comprises four(4) photodiodes 1530. In sensor 1528, each individual photodiode 1530 iscoupled to a respective transimpedance amplifier 1532. The output of theamplifiers 1532 may then be aggregated into averaging circuit 1520 toproduce a signal.

As noted previously, one skilled in the art will recognize that thephotodiodes and detectors may be arranged in different fashions tooptimize the detected light. For example, sensor 1534 illustrates anexemplary “4 PD per stream” sensor in which the detectors 106 comprisephotodiodes 1536 arranged in a linear fashion. Likewise, sensor 1538illustrates an exemplary “1 PD per stream” sensor in which the detectorscomprise photodiodes 1540 arranged in a linear fashion.

Alternatively, sensor 1542 illustrates an exemplary “4 PD per stream”sensor in which the detectors 106 comprise photodiodes 1544 arranged ina two-dimensional pattern, such as a zig-zag pattern. Sensor 1546illustrates an exemplary “1 PD per stream” sensor in which the detectorscomprise photodiodes 1548 also arranged in a zig-zag pattern.

FIG. 15L illustrates an exemplary architecture for aswitched-capacitor-based front-end. As shown, front-end interfaces 108may be implemented using switched capacitor circuits and any number offront-end interfaces 108 may be implemented. The output of theseswitched capacitor circuits may then be provided to a digital interface1000 and signal processor 110. Switched capacitor circuits may be usefulin system 100 for their resistor free design and analog averagingproperties. In particular, the switched capacitor circuitry provides foranalog averaging of the signal that allows for a lower smaller samplingrate (e.g., 2 KHz sampling for analog versus 48 KHz sampling for digitaldesigns) than similar digital designs. In some embodiments, the switchedcapacitor architecture in front end interfaces 108 may provide a similaror equivalent SNR to other front end designs, such as a sigma deltaarchitecture. In addition, a switched capacitor design in front endinterfaces 108 may require less computational power by signal processor110 to perform the same amount of decimation to obtain the same SNR.

FIGS. 16A and 16B illustrate embodiments of disposable optical sensors1600. In an embodiment, any of the features described above, such asprotrusion, shielding, and/or heat sink features, can be incorporatedinto the disposable sensors 1600 shown. For instance, the sensors 1600can be used as the sensors 101 in the system 100 described above withrespect to FIG. 1. Moreover, any of the features described above, suchas protrusion, shielding, and/or heat sink features, can be implementedin other disposable sensor designs that are not depicted herein.

The sensors 1600 include an adult/pediatric sensor 1610 for fingerplacement and a disposable infant/neonate sensor 1602 configured fortoe, foot or hand placement. Each sensor 1600 has a tape end 1610 and anopposite connector end 1620 electrically and mechanically interconnectedvia a flexible coupling 1630. The tape end 1610 attaches an emitter anddetector to a tissue site. Although not shown, the tape end 1610 canalso include any of the protrusion, shielding, and/or heat sink featuresdescribed above. The emitter illuminates the tissue site and thedetector generates a sensor signal responsive to the light after tissueabsorption, such as absorption by pulsatile arterial blood flow withinthe tissue site.

The sensor signal is communicated via the flexible coupling 1630 to theconnector end 1620. The connector end 1620 can mate with a cable (notshown) that communicates the sensor signal to a monitor (not shown),such as any of the cables or monitors shown above with respect to FIGS.2A through 2D. Alternatively, the connector end 1620 can mate directlywith the monitor.

FIG. 17 illustrates an exploded view of certain of the components of thesensor 301 f described above. A heat sink 1751 and a cable 1781 attachto an emitter shell 1704. The emitter shell attaches to a flap housing1707. The flap housing 1707 includes a receptacle 1709 to receive acylindrical housing 1480/1580 (not shown) attached to an emittersubmount 1702, which is attached to a circuit board 1719.

A spring 1787 attaches to a detector shell 1706 via pins 1783, 1785,which hold the emitter and detector shells 1704, 1706 together. Asupport structure 1791 attaches to the detector shell 1706, whichprovides support for a shielding enclosure 1790. A noise shield 1713attaches to the shielding enclosure 1790. A detector submount 1700 isdisposed inside the shielding enclosure 1790. A finger bed 1710 providesa surface for placement of the patient's finger. Finger bed 1710 maycomprise a gripping surface or gripping features, which may assist inplacing and stabilizing a patient's finger in the sensor. A partiallycylindrical protrusion 1705 may also be disposed in the finger bed 1710.As shown, finger bed 1710 attaches to the noise shield 1703. The noiseshield 1703 may be configured to reduce noise, such as from ambientlight and electromagnetic noise. For example, the noise shield 1703 maybe constructed from materials having an opaque color, such as black or adark blue, to prevent light piping.

Noise shield 1703 may also comprise a thermistor 1712. The thermistor1712 may be helpful in measuring the temperature of a patient's finger.For example, the thermistor 1712 may be useful in detecting when thepatient's finger is reaching an unsafe temperature that is too hot ortoo cold. In addition, the temperature of the patient's finger may beuseful in indicating to the sensor the presence of low perfusion as thetemperature drops. In addition, the thermistor 1712 may be useful indetecting a shift in the characteristics of the water spectrum in thepatient's finger, which can be temperature dependent.

Moreover, a flex circuit cover 1706 attaches to the pins 1783, 1785.Although not shown, a flex circuit can also be provided that connectsthe circuit board 1719 with the submount 1700 (or a circuit board towhich the submount 1700 is connected). A flex circuit protector 1760 maybe provided to provide a barrier or shield to the flex circuit (notshown). In particular, the flex circuit protector 1760 may also preventany electrostatic discharge to or from the flex circuit. The flexcircuit protector 1760 may be constructed from well known materials,such as a plastic or rubber materials.

FIG. 18 shows the results obtained by an exemplary sensor 101 of thepresent disclosure that was configured for measuring glucose. Thissensor 101 was tested using a pure water ex-vivo sample. In particular,ten samples were prepared that ranged from 0-55 mg/dL. Two samples wereused as a training set and eight samples were then used as a testpopulation. As shown, embodiments of the sensor 101 were able to obtainat least a standard deviation of 13 mg/dL in the training set and 11mg/dL in the test population.

FIG. 19 shows the results obtained by an exemplary sensor 101 of thepresent disclosure that was configured for measuring glucose. Thissensor 101 was tested using a turbid ex-vivo sample. In particular, 25samples of water/glucose/Lyposin were prepared that ranged from 0-55mg/dL. Five samples were used as a training set and 20 samples were thenused as a test population. As shown, embodiments of sensor 101 were ableto obtain at least a standard deviation of 37 mg/dL in the training setand 32 mg/dL in the test population.

FIGS. 20 through 22 shows other results that can be obtained by anembodiment of system 100. In FIG. 20, 150 blood samples from twodiabetic adult volunteers were collected over a 10-day period. Invasivemeasurements were taken with a YSI glucometer to serve as a referencemeasurement. Noninvasive measurements were then taken with an embodimentof system 100 that comprised four LEDs and four independent detectorstreams. As shown, the system 100 obtained a correlation of about 85%and Arms of about 31 mg/dL.

In FIG. 21, 34 blood samples were taken from a diabetic adult volunteercollected over a 2-day period. Invasive measurements were also takenwith a glucometer for comparison. Noninvasive measurements were thentaken with an embodiment of system 100 that comprised four LEDs inemitter 104 and four independent detector streams from detectors 106. Asshown, the system 100 was able to attain a correlation of about 90% andArms of about 22 mg/dL.

The results shown in FIG. 22 relate to total hemoglobin testing with anexemplary sensor 101 of the present disclosure. In particular, 47 bloodsamples were collected from nine adult volunteers. Invasive measurementswere then taken with a CO-oximeter for comparison. Noninvasivemeasurements were taken with an embodiment of system 100 that comprisedfour LEDs in emitter 104 and four independent detector channels fromdetectors 106. Measurements were averaged over 1 minute. As shown, thetesting resulted in a correlation of about 93% and Arms of about 0.8mg/dL.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or states are included or are to beperformed in any particular embodiment.

While certain embodiments of the inventions disclosed herein have beendescribed, these embodiments have been presented by way of example only,and are not intended to limit the scope of the inventions disclosedherein. Indeed, the novel methods and systems described herein can beembodied in a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein can be made without departing from the spirit of theinventions disclosed herein. The claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of certain of the inventions disclosed herein.

1. A physiological, noninvasive detector configured to detect opticalradiation from a tissue site, said detector comprising: a set ofphotodetectors that each provide a signal stream indicating opticalradiation from the tissue site, wherein the set of photodetectors arearranged in a spatial configuration that provides a variation in pathlengths between at least some of the photodetectors; and a conversionprocessor that provides information indicating an analyte in the tissuesite based on ratios of pairs of the signal streams.
 2. The detector ofclaim 1, wherein the set of photodetectors are contained in opticallyseparate compartments.
 3. The detector of claim 1, wherein theconversion processor comprises a set of transimpedance amplifiers thatconvert the signals from the photodetectors into a signal having arespective stream for each photodetector.
 4. The detector of claim 1,wherein the conversion processor comprises a set of switched capacitorcircuits configured to convert the signals from the photodetectors intoa digital signal having a respective stream for each photodetector. 5.The detector of claim 1, wherein the set of photodetectors are arrangedin a two-dimensional grid.
 6. The detector of claim 1, wherein the setof photodetectors are arranged in a row.
 7. The detector of claim 1,wherein the set of photodetectors are arranged in a row having differentseparation distances.
 8. The detector of claim 1, wherein the set ofphotodetectors are arranged in a row having decreasing separationdistances.
 9. The detector of claim 1, wherein the set of photodetectorscomprise a set of four photodiodes coupled together.
 10. The detector ofclaim 1, wherein the photodetector in the set of photodetectors comprisea set of two photodiodes coupled together.
 11. The detector of claim 1,wherein the photodetector in the set of photodetectors comprise a set ofthree photodiodes coupled together.
 12. The detector of claim 1, whereinthe photodetector in the set of photodetectors comprise a set of fourphotodiodes coupled together.
 13. The detector of claim 1, wherein thephotodetector in the set of photodetectors comprise a set of ninephotodiodes coupled together.